Binder system and method for particulate material with debind rate control additive

ABSTRACT

The present invention relates to a binder composition comprising a polycarbonate polymer; an ethylenebisamide wax; a guanidine wetting agent, and an additive which accelerates or delays completion of debinding of the binder composition. The present invention further relates to a method for forming a sintered part by powder injection molding, including the steps of forming a green composition comprising a binder and an inorganic powder, wherein binder is a composition comprising a polycarbonate polymer, an ethylenebisamide wax, a guanidine wetting agent and an additive which accelerates or delays completion of debinding of the binder; melting the composition; injecting the composition into a mold for a part; heating the part to a temperature at which the binder decomposes; heating the part to a temperature at which the inorganic powder is sintered. The binder composition of the present invention is useful for press and sinter applications as well as for powder injection molding applications.

FIELD OF THE INVENTION

The present invention relates to binder compositions for use in formingsintered parts by powder injection molding and to green compositions ofthe binder composition and inorganic powders, in which the bindercompositions may include additional components which provide a broaderrange of control of reverse debinding, and to methods of using suchbinder compositions. The binders of the present invention require fewersteps to produce a part, have higher thixotropic energy, melt at a lowertemperature, provide a green body having high strength, and decomposethermally in a clean, substantially ash-free burnout to yield simple,environmentally safe products, and may further include additives bywhich the rate and final temperature of debinding may be selected andcontrolled.

BACKGROUND OF THE INVENTION

Processes for forming shaped articles from particulate mixtures areknown in the art. Classically, a desired particulate material is mixedwith a binder and then formed into the desired shape, this being calleda green body. The green body is then fired to provide a fusion of theparticulate material and to drive off the binder, thereby producing thedesired shaped product with proper surface texture, strength, etc.Modern methods include press and sinter (P&S) and powder injectionmolding (PIM). In P&S, a mixture of one or more of a metal, metal oxide,intermetallic or ceramic powder and a small amount of binder (about1-10%, or, on average, about 5% of the powder volume) are placed in arelatively simple mold, pressed into a green body, and then sintered.The small amount of binder is decomposed during the sintering step, so aseparate step of removing the binder is not necessary. However, P&S islimited to simple parts.

In PIM, a mixture of one or more of a metal, metal oxide, intermetallicor ceramic powder and a quantity of binder from 30% to 60% of the volumeof powder are heated to a liquid state and then injected under pressureinto a mold to form a part. Once in the mold, the binder is removed inone or more steps and the part is fired to sinter the particles into asolid part. PIM is capable of producing quite complex parts.

In the production of shaped objects by PIM in the manner abovedescribed, it has been found that the binder, while necessary to theprocess, create problems. The binder must be used in order to form anobject of practical use, but most of it must be removed before the partcan be sintered, although in some cases a portion of the binder remainsuntil sintering is completed.

Direct removal of the PIM binder during sintering is problematic. Manybinders leave behind ash upon decomposition. When such ash combines withcertain ingredients in the powder component, eutectic mixtures may beformed. Such eutectic compounds as TiC may be formed from titanium andcarbon ash, and these can result in serious problems in the formed part.

Thermoplastic binders which decompose on heating have been used.However, these materials tend to soften or melt first and thendecompose, creating problems on decomposition. Thermoplastic materialshave been tried which decompose below their melting point and therebyremain in place until decomposition. Binders have been removed byexposure to a decomposing atmosphere, such as an acid atmosphere todecompose an acid-labile organic binder. The drawback of this approachis the use of an acid atmosphere, requiring a special chamber andhazardous material handling capabilities. Binders which are subject tocatalytic decomposition also have been used, such as a polyacetal. Thedrawback of this approach is that the decomposition product isformaldehyde, which also requires special equipment to collect anddecompose the formaldehyde.

The prior art has recognized this problem and has therefore attempted toremove the binder from the shaped green body prior to the step ofsintering. Such processes have used various solvents, including organicsolvents, triple-point CO₂, and water to dissolve and remove the binder.While systems using such procedures can provide advantages overprocedures wherein the binder is removed during firing, articles formedby removing the binder prior to firing still have the tendency to crackduring the binder removal as well as during the firing operation. Onereason for this is that the binder is removed from the green body bymeans of a solvent when the binder is in the solid state, and upondissolution the binder, the binder-solvent mixture has a tendency toexpand. This problem has been approached by various means, includingheating the green body prior to exposing it to the solvent, by using asolvent to remove a portion of the binder and removing the remainder byfiring, and by using a two-part binder, each part of which is soluble ina different solvent, so each solvent removes a portion of the binder,and by using the different solvents in a stepwise manner. Each of thesemethods includes its own drawbacks. All of these solvent-based methodssuffer from the necessity of dealing with the solvents and the problemsinherent therein, such as toxicity, recycling, evaporation losses andenvironmental considerations.

Thus, the need remains for binders which are useful, particularly inpowder injection molding, which require a minimum number of steps toremove, which have high thixotropic energy, which melt at a lowtemperatures, which provide a green body having high strength, and whichdecompose thermally to yield simple, environmentally safe products,substantially free of ash, thereby yielding a binder which performs itsfunction but which provides a process of powder injection molding whichproceeds with a minimum number of process steps, can be carried out inan air atmosphere in many cases, and does not leave behind deleteriousresidues, either in the part or in the environment.

In addition to the foregoing needs, there exists a need for furthercontrol of the debinding process, by which the debinding time andtemperature can be adjusted and controlled to match the characteristicsof the inorganic material of which the green composition is comprised.

SUMMARY OF THE INVENTION

The present invention requires only simple, standard equipment which isinexpensive and commonly available. The steps of debinding and sinteringmay be carried out in the same equipment, on a continuous basis, therebyavoiding downtime for cooling and transfer from debinding equipment tosintering equipment.

In one embodiment, the present invention relates to a binder compositioncomprising a polycarbonate polymer; an ethylenebisamide wax; a guanidinewetting agent; and an additive which in use accelerates or extendsdebinding of the binder composition. The present invention furtherrelates to a method for forming a part by powder injection molding,including the steps of forming a green composition comprising a binderand an inorganic powder, wherein the binder is a composition comprisinga polycarbonate polymer, an ethylenebisamide wax, a guanidine wettingagent and an additive; heating the green composition to debind the greencomposition, wherein the additive accelerates or extends the debindingstep. In one embodiment, the additive is an debinding accelerator whichincreases the rate of debinding of at least one of the first threeelements of the binder composition. In one embodiment, the additive isan debinding accelerator which increases debinding of at least one ofthe first three elements of the binder composition. In one embodiment,the additive is a debinding extender which extends the time and/orincreases the upper temperature of, the debinding process.

In one embodiment, the binder composition of the present invention mayinclude both an debinding accelerator and a debinding extender. Thedebinding accelerator assists in quickly dispensing with thelower-temperature-debinding components of the composition, while thedebinding extender extends the debinding and thereby assures that atleast some of the components of the debinding composition remain tomaintain the inorganic powder particles in place in the mold until theonset of sintering.

Thus, the binder composition and method of making sintered parts usingthe binder composition of the present invention provide the featuresmissing from the prior art. The binder composition may be removed in aminimum number of steps, has high thixotropic energy, melts and becomesflowable at a low temperature, provides a green body having highstrength, and decomposes thermally to yield simple, environmentally safeproducts, substantially free of ash. In addition, the additive allowsincreased control of the timing and temperature of the debinding stepsas compared to a binder without the additive. When the additive is andebinding accelerator, the time required for debinding can be reduced.When the additive is a debinding extender, the time and/or temperatureof debinding can be increased. The binder composition thereby performsits function while providing a process of powder injection molding whichproceeds with a minimum number of steps, can be debound in air,hydrogen, oxygen, argon, nitrogen and similar gas atmospheres or invacuum, and does not leave behind deleterious residues, either in thepart or in the environment, and does so in a more controllable manner,adapted to correspond to the inorganic components to be bound and formedinto the desired part, and while providing increased control of thedebinding process. The debinding accelerator may be used advantageouslyto increase the rate of the initial debinding steps, and thereby toreduce overall production time. The tie molecule may be used toadvantageously extend the completion of the debinding steps, and therebyassure that the inorganic powder retains its desired form until theonset of sintering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the steps in a method of making a partby powder injection molding in accordance with the present invention.

FIG. 2 is a schematic engineering drawing of one screw of a twin screwcompounding extruder in accordance with one embodiment of the invention.

FIG. 3 is a graph of a debinding profile of an exemplary greencomposition which does not contain an additive.

FIG. 4 is a graph of a debinding profile of an exemplary greencomposition, similar to that of FIG. 2, but which contains an debindingaccelerator, according to the present invention.

FIG. 5 is a graph of a debinding profile of an exemplary greencomposition, similar to that of FIG. 2, but which contains a debindingextender, according to the present invention.

FIG. 6 is a graph of a debinding profile of an exemplary greencomposition, similar to that of FIG. 2, but which contains both andebinding accelerator and a debinding extender, according to the presentinvention.

DETAILED DESCRIPTION

The binder composition and the green composition comprising the bindercomposition and an inorganic powder, each in accordance with the presentinvention, are applicable both to powder injection molding (PIM)techniques and to press and sinter (P&S) applications. In PIM, a greencomposition or feedstock comprising an inorganic powder and a bindercomposition is used for powder injection molding, which includes stepsof debinding and sintering. In P&S applications, a green compositioncomprising an inorganic powder and a binder composition are pressed intoa mold and sintered to form a part, without a step of debinding. Theinorganic powders which may be used in the green compositions and methodof the present invention may be metal, metal oxide, intermetallic and/orceramic, or mixtures of these, depending upon the desiredcharacteristics of the final product. The green composition comprisingan inorganic powder and binder composition of the present invention, maybe injection molded with an increased loading of the inorganic powdercompared to prior processes, resulting in less shrinkage and deformationduring debinding and sintering. The components of the binder compositionallow debinding of the nascent part with decomposition of the binder toyield environmentally safe products in a relatively rapid, controllableprocess, thereby efficiently overcoming the deficiencies of the priorart.

The components of the binder composition are partially miscible with oneanother, such that when the green composition is ready for use, thecomponents thereof are sufficiently miscible that the desired parts areformed when the composition is pumped into the mold, but the componentsare sufficiently immiscible that the phases can separate and thecomponents will “come apart” in a step-wise, controllable manner in anoven or kiln during the debinding step. The binder composition of thepresent invention may be removed thermally, in the same oven or chamberin which the part is sintered, thereby avoiding a multiple oven,multiple step process of debinding and sintering the part

The present inventor have discovered that, in addition to the componentsof the binder composition controllably debinding in an order which isthe opposite of that normally sought in the PIM industry, by judicioususe of the presently disclosed additives, the rate and/or temperature ofdebinding can be further adjusted and controlled. In conventional bindercompositions, which include, e.g., stearic acid as a surface agent,paraffin wax as the wax, and polypropylene as the major bindercomponent, during the debinding step of a PIM process, the surface agentreleases first, the wax component releases next, and the major bindercomponent releases last. The conventional binder compositions not onlydebind in this order, but the rate of debinding is difficult to adjust,and cannot provide a reverse debind, in which the surface agent is thelast component to debind.

The components of the binder composition of the present invention, incontrast, release in the opposite order, and provide control in the rateand/or temperature of debinding. In the binder composition of thepresent invention, the major binder component, a polycarbonate polymer,has a decomposition temperature of about 185° C. The wax component, anethylenebisamide wax, has a decomposition temperature of about 285° C.The guanidine wetting or surface agent is the last component todecompose, having a decomposition temperature in the range of about 350°C. to about 450° C. When an debinding accelerator is the additive,according to the present invention, the time required for, e.g., thepolycarbonate polymer to debind, can be selectively reduced. When adebinding extender is the additive, according to the present invention,the time and/or temperature required for the debinding to be completedcan be selectively increased. Thus, according to the present invention,during the debinding step of a PIM process, the components of the bindercomposition debind in an order opposite to that of conventional bindercompositions, and the time and/or temperature of debinding can becontrollably adjusted.

As a result of the debinding profile of the binder composition accordingto the present invention, the surface agent, is the last of the firstthree primary binder ingredients (polycarbonate, ethylenebisamide waxand surface agent) to decompose in the debinding step. When the additiveis an debinding accelerator, the surface agent still is the last todecompose. However, when the additive is a debinding extender, thedebinding extender debinds after the surface agent, extending the timeand/or increasing the final temperature of debinding. As a result, whena debinding extender is the additive, the inorganic powder is retainedin position for a longer time in the pre-sintering portion of theprocess. Retaining the inorganic powder particles in position for alonger time provides the benefit of allowing the transition fromdebinding to sintering to occur with a significantly reduced possibilitythat the inorganic powder particles will move or be distorted from theiroriginal position in the mold, and, in the case of certainhigh-temperature-sintering ceramics and high-temperature-melting metals,provides an extended time and/or temperature of binding, so that theparticles are held in place by the binder for a longer time and to ahigher temperature, allowing them to begin to sinter in their intendedposition. As a result, superior sintered parts are obtained from the PIMprocess using the binder composition of the present invention.

The debinding accelerator provides increased production rates. For manyceramics, no sintering takes place at lower temperatures, such as thedebinding temperature of the polycarbonate, and the other componentsprovide adequate binding to the part once it has been placed in themold. The polycarbonate needs to be a relatively high-melting polymer,however, in order to remain as a solid at mildly elevated temperatures.A lower molecular weight polycarbonate would not provide sufficientbinding. However, once the part is transferred into the mold, thepolycarbonate binder is no longer needed for this function. Thus, thepolycarbonate should be debound as rapidly as possible.

However, some time is required for the polycarbonate to be debound fromthe green composition. While the inventors will not be bound by theory,it is believed that debinding of the polycarbonate takes place via lossof individual molecules of carbonate monomers from the free ends of thepolycarbonate polymer chains. This process is referred to herein as“unzipping”. In this scenario, individual monomer molecules are lostonly from the free ends of the polymer chains, and the more free ends,the faster the debinding. The debinding accelerator is added to increasethe rate of debinding, by breaking the polycarbonate polymer chains intoshorter polymer chains, thus increasing the number of free ends,increasing the loss of monomers, thereby resulting in more rapiddebinding. The process of breaking the polymer chains into shorterpolymer chains is referred to herein as “chain scission”. The debindingaccelerator may be any molecule which cuts or scissions the polymerchains into shorter polymer chains. In one embodiment the debindingaccelerator is a free radical generating molecule, such as a peroxide.

In one embodiment, the debinding accelerator is a free radical generatorapplied from an external source, such as ozone, gamma radiation orelectron beam, which introduces free radicals from which polymerscission results.

When the ceramic or metal in the green composition to be formed into apart requires a temperature significantly higher than the debindingtemperature of the guanidine wetting agent, problems may result. This isdue to the fact that at an interim time when all or substantially all ofthe binder has been debound from the green composition, and theinorganic component of the green composition has not yet begun tosinter, there is nothing to hold the particles of the inorganiccomponent together or in the relationship established in the greencomposition, which creates the problem. The problem is that during theinterim time, the particles of the inorganic component may collapse orform voids, both of which result in a faulty part. The embodiment of thepresent invention in which the additive is a debinding extender isintended to address and solve this problem.

The debinding extender is a molecule which has a higher debindingtemperature than the highest-temperature debinding component of theoriginal three components, which is the guanidine wetting agent. Theguanidine wetting agent has a debind temperature such that by the timethe part reaches 450° C., all or substantially all of the guanidinewetting agent has been debound and is gone. The debinding extender has adebind temperature generally in the range from about 450° C. to about850° C. The exact debind temperature of the debinding extender can beselected according to the temperature at which sintering begins in thehigh-temperature-sintering component of the green composition. Thus thedebind temperature of the debinding extender will match or correspond tothe temperature at which sintering of the inorganic powder begins. Thus,the part will remain bound until sintering is initiated. Since thedebinding extender debinds at a higher temperature, it will generallyrequire a longer time for a green composition containing the debindingextender as the additive to debind.

The partial miscibility of the components of the binder compositionfacilitates the reverse debinding of the present invention. Since thepolycarbonate polymer is only partially miscible with the othercomponents and has a lower glass transition (T_(g)) and melting ordecomposition temperature, it can melt and separate from the othercomponents of the binder composition, then wick out of the green partfirst. Addition of an debinding accelerator as the additive results inchain scission of the polycarbonate into shorter polymer chains, andmore rapid unzipping of the remaining polymer chains, as a result ofwhich the polycarbonate is debound more rapidly than it would otherwisehave been. When the polycarbonate component has been removed, thetemperature may be raised to a temperature at which the next componentmay be debound. In the present invention, following polycarbonate, theethylenebisamide is the next component to decompose or be debound. Againthe partial miscibility of the components aids the separation, allowingthe ethylenebisamide to decompose without affecting the guanidinewetting agent. When the ethylenebisamide has been removed, only theguanidine wetting agent remains. At this time, the temperature is againincreased to the decomposition temperature of the guanidine wettingagent, which is in the range from about 350° C. to about 450° C.,depending on the exact nature of the guanidine wetting agent, i.e.,which acid has been reacted with guanidine to form the guanidine wettingagent. Once the guanidine wetting agent has been debound, the remaininginorganic powder may be sintered to form the desired final part. In anembodiment in which a debinding extender has been added as the additive,the debinding extender debinds subsequent to the debinding of theguanidine wetting agent, but the debinding is extended to thetemperature of onset of sintering of the inorganic powder component ofthe green composition. The temperature of debinding of the debindingextender may be in the range from about 450° C. to about 850° C.

The binder composition of the present invention comprises apolycarbonate polymer, a wax such as ethylenebisamide wax, a guanidinewetting agent, and an additive. Each of these three general componentmaterials, and each of the additives are more fully disclosed in thefollowing.

Guanidine Wetting Agent

In one embodiment, the guanidine wetting agent is a reaction product ofguanidine and an acid selected from a fatty acid, an organic acid, acidand a stronger acid such as an alkyl sulfonic acid. The guanidinewetting is a reaction product which may be an amide or actually may bemore in the nature of a hydrated salt. For example, according to the CRCHandbook of Chemistry and Physics, 74^(th) Ed., guanidine acetate hasthe formula (H₂N)₂C═NH.CH₃COOH, rather than an amide-type formula suchas H₂N—C═NH(NH)COCH₃, as would be expected for an amide. This is due tothe fact that guanidine is a very strong base, and is much more likelyto simply abstract a proton from a relatively weak organic acid, ratherthan react with the organic acid in a “standard” amidization reactionforming an amide with concomitant loss of H₂O. However, in some cases,the reaction of guanidine and the acid may yield an amide in the“standard” manner. For this reason, the guanidine surface agent of thepresent invention will be referred to herein as the reaction product ofguanidine and an acid. The term “reaction product of guanidine and anacid” includes both of the above-described forms of the product of areaction between or mixture of guanidine and an acid, and mixtures ofthese forms or other possible forms.

The particular acid used to make the reaction product of guanidine andan acid is selected based upon the surface charge of the inorganicpowder with which the binder composition is to be used. In oneembodiment, the guanidine wetting agent is guanidine stearate. Guanidinestearate and guanidine compounds of similar acids are selected for usewith powders having a positive surface charge and an isoelectric pointat a low pH. In one embodiment, the guanidine wetting agent is guanidineethyl-hexanoate. Guanidine ethyl-hexanoate and guanidine compounds ofsimilar acids are selected for use with powders having an amphotericsurface charge, and an isoelectric point at a near-neutral pH. In oneembodiment, the guanidine wetting agent is guanidine lauryl sulfonate.Guanidine lauryl sulfonate and guanidine compounds of similar acids areselected for use with powders having a negative surface charge, and anisoelectric point at a high pH. In other embodiments, the guanidinewetting agent may be the reaction product of guanidine and other acids.The selection of the appropriate acid for preparation of the reactionproduct of guanidine and an acid depends upon the isoelectric point ofthe inorganic powder. The relationship is further described in thefollowing detailed description. The many acids which may be reacted withthe guanidine to form the reaction product of guanidine and an acid aredescribed in detail hereafter.

In general, the appropriate acid depends on the surface charge, or pointof zero charge (PZC), which may be expressed as the isoelectric point(IEP) of the inorganic powder with which the binder composition is to beused in the green composition. Isoelectric points may be found inreference sources, or may be determined experimentally, by determiningthe pH at which no charge exists on the powder particle. The point ofzero charge is the average of the pK's for the particular powder, andindicates the average acid-base character of the surface. Isoelectricpoints of a number of ceramic oxide materials are shown in the followingtable:

TABLE Isoelectric Points of Oxides Material Nominal Composition IEPMuscovite KAl₃Si₃O₁₁H₂O₁₁ 1 Quartz SiO₂ 2 Delta manganese oxide MnO₂ 2Soda lime silica glass 1.00 Na₂O 2-3 0.58 CaO 3.70 SiO₂ AlbiteNa₂OAl₂O₃6SiO₂ 2 Orthoclase K₂OAl₂O₃6SiO₂ 3-5 Silica (amorphous) SiO₂3-4 Zirconia ZrO₂ 4-5 Rutile TiO₂ 4-5 Tin Oxide SnO₂ 4-7 Apatite10CaO6PO₂2H₂O 4-6 Zircon SO₂ZrO₂ 5-6 Anatase TiO₂ 6 Magnetite Fe₃O₄ 6-7Hematite αF₃O₃ 6-9 Goethite FeOOH 6-7 Gamma iron oxide γFe₂O₃ 6-7 Kaolin(edges) Al₂O₃SiO₂2H₂O 6-7 Chromium oxide αCr₂O₃ 6-7 Mullite 3Al₂O₃2SiO₂7-8 Gamma alumina γAl₂O₃ 7-9 Alpha alumina αA1₂O₃   9-9.5 Alumina (Bayerprocess) Al₂O₃   7-9.5 Zinc oxide ZnO₂ 9 Copper oxide CuO 9 Bariumcarbonate BaCO₃ 10-11 Yttria Y₂O₃ 11  Lathanum oxide La₂O₃ 10-12 Silveroxide Ag₂O 11-12 Magnesium Oxide MgO 12-13 Source: Temple C. Patton,Paint Flow and Pigment Dispersion, Wiley-Interscience. New York, 1979;E. G. Kelly and D. J. Spottiswood, Introduction to Mineral Processing,Wiley-Interscience, New York, 1982; 1. M. Cases, Silic. Ind., 36, 145(1971); R. H. Toon, T. Salman, and G. Donnay, J. Colloid Interface Sci.,70, 483 (1979).

According to the present invention, the reaction product of guanidineand organic acids in the C₁₂ to C₂₂ range are used with materials havinga low isolectric point, i.e., which have a low pH at the point of zerocharge. Thus, for example the reaction product of guanidine and oleicacid (C₁₇H₃₃CO₂H) would be suitable for use with quartz powder (SiO₂),which has an IEP of 2, according to Table 1 above. Other suitable acidsfor use with inorganic powders having a low isoelectric point includesuch saturated fatty acids as (common names in parentheses) dodecanoic(lauric) acid, tridecanoic (tridecylic) acid, tetradecanoic (myristic)acid, pentadecanoic (pentadecylic) acid, hexadecanoic (palmitic) acid,heptadecanoic (margaric) acid, octadecanoic (stearic) acid, eicosanoic(arachidic) acid, 3,7,11,15-tetramethylhexadecanoic (phytanic) acid,monounsaturated, diunsaturated, triunsaturated and tetraunsaturatedanalogs of the foregoing saturated fatty acids.

According to the present invention, the reaction product of guanidineand organic acids in the C₆ to C₁₂ range are used with materials havinga mid-range isolectric point, i.e., which have a pH around 6 at thepoint of zero charge. These materials may also be referred to asamphoteric. For example, the reaction product of guanidine and anorganic acid such as ethylhexanoic acid (C₇H₁₅CO₂H) would be suitablefor use with an inorganic powder having an IEP of about 6.0, for examplewith zircon (SiO₂.ZrO₂), which has an IEP of 5-6, or anatase (TiO₂),which has an IEP of 6, each according to Table 1 above. Hexanoic acid,heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoicacid are other straight-chain carboxylic acids which may be reacted withguanidine for use with inorganic powders having a mid-range isoelectricpoint. Branched-chain carboxylic acids in the C₆ to C₁₂ range may alsobe used with materials having a mid-range isolectric point.

According to the present invention, the reaction product of guanidineand stronger acids such as sulfonates, phthalates, benzoates, phosphatesand phenols are used with materials having a high isolectric point,i.e., which have a pH around 10-12 at the point of zero charge. Forexample, the reaction product of guanidine and an acid such asbenzenesulfonic acid may be used with an inorganic powder such as silveroxide, which has an IEP of 11-12, as shown in Table 1 above.

According to the present invention, for materials having intermediateIEPs, such as, for example, mullite (3Al₂O₃.2SiO₂), IEP=7-8, a mixtureof guanidine wetting agents may be used. As an alternative, intermediateacids may be selected for reaction with guanidine. Thus, for example, ifmullite is the inorganic powder, the guanidine wetting agent used in thebinder composition therewith may be a mixture of the reaction product ofguanidine and benzenesulfonic acid and the reaction product of guanidineand ethylhexanoic acid. Alternatively, for mullite, the guanidinewetting agent used in the binder composition therewith may be thereaction product of guanidine and a weaker acid such as benzoic acid maybe used.

Similarly, according to the present invention, for materials havingintermediate IEPs, such as, for example, amorphous silica (SiO₂),IEP=3-4, a mixture of guanidine wetting agents may be used. As analternative, intermediate acids may be selected for reaction withguanidine. Thus, for example, if silica is the inorganic powder, theguanidine wetting agent used in the binder composition therewith may bea mixture of the reaction product of guanidine and octadecanoic(stearic) acid and the reaction product of guanidine and ethylhexanoicacid. Alternatively, for silica, the guanidine wetting agent used in thebinder composition therewith may be the reaction product of guanidineand dodecanoic acid may be used. Dodecanoic acid, C₁₁H₂₃CO₂H, appears inboth groups of acids, those for use with the low IEP powders and thosefor use with intermediate IEP powders. The intermediate character ofsuch an acid makes it suitable for use with an intermediate IEP powder.

While a certain amount of trial and error may be required to optimizethe reaction product of guanidine and an acid for a particular inorganicpowder, and particulary for a combination of inorganic powders, theselection can be guided by the foregoing disclosure. Thus, the low IEPpowders work best with a “very fatty”, relatively weak acid,intermediate IEP powders work best with a mid-range organic acid, andthe high EIP powders work best with a stronger acid having relativelyless organic character, such as an alkyl sulfonic acid. The acidselected should be rheologically compatible with the compounding andinjection molding equipment. Some testing may be required in order tooptimize the acid for reaction with guanidine to form the guanidinewetting agent for a given inorganic powder.

Polycarbonate Polymer

In the binder composition of the present invention, the polycarbonatepolymer is a low molecular weight polycarbonate polymer. In oneembodiment, the polycarbonate polymer is poly(propylene carbonate).Poly(propylene carbonate) is prepared from the reaction of carbondioxide, CO2, and propylene oxide, CH₂═CH(O)CH₂, as shown in thefollowing:

The poly(propylene carbonate) shown above, on application of sufficientheat, decomposes cleanly into the following, which is a liquid having aboiling point near the decomposition temperature of the poly (propylenecarbonate):

In one embodiment, the polycarbonate polymer has a number averagemolecular weight in the range from about 25,000 to about 75,000. In oneembodiment, the polycarbonate polymer has a number average molecularweight in the range from about 35,000 to about 65,000. In oneembodiment, the polycarbonate polymer has a number average molecularweight in the range from about 35,000 to about 40,000. In oneembodiment, the polycarbonate polymer has a number average molecularweight of about 50,000. In one embodiment, the polycarbonate polymer hasa number average molecular weight in the range from about 45,000 toabout 55,000.

In one embodiment, the polycarbonate polymer is Q-PAC™ 40, availablefrom PAC Polymers, a division of Axcess Corporation, Newark, DE. Q-PAC™40 is a low molecular weight polycarbonate, having a number averagemolecular weight in the range of about 50,000. Q-PAC™ 40 has a glasstransition temperature, T_(g)=40° C. Q-PAC™ 40 is a low boiling liquid,having a boiling point of 242° C. Thus, at relatively moderatetemperatures, Q-PAC™ 40 melts and may exit the green form as a liquidhaving only a slightly increased volume with respect to the solid,rather than decomposing into a gas having a greatly increased volumewith respect to the solid. As above, the partial miscibility of thepolycarbonate polymer allows it to melt and separate from the remainingcomponents of the green composition during the debinding process.

The decomposition product of poly(propylene carbonate) is shown above.This cyclic propylene carbonate has a melting point below thetemperature at which the polymer decomposes. Thus, as the bindercomposition of the present invention, when mixed with the inorganicpowder to form the green composition and injected into a mold, isheated, the poly(propylene carbonate) first melts and then begins todecompose into the liquid cyclic propylene carbonate shown above. Onfurther heating in the debinding process, the cyclic propylene carbonatedecomposes cleanly in air to form CO₂ and water. Thus, according to thepresent invention, the polycarbonate polymer is the first component tobe lost from the green composition in the debinding process. Incontrast, in the prior art binders, the polymeric component has beendesigned to be the last component lost from the binder during thedebinding process.

Ethylenebisamide Wax

The binder composition of the present invention includes anethylenebisamide wax. The ethylenebisamide wax is a wax formed by theamidization reaction of ethylene diamine and a fatty acid. The fattyacid of the bisamide wax may be any fatty acid in the range from C₁₂ toabout C₂₂, and may be saturated or unsaturated. In one embodiment, thefatty acid is stearic acid, a saturated C₁₈ fatty acid. Thus, in oneembodiment, the ethylenebisamide wax is ethylenebisstearamide wax.Ethylenebisstearamide has a discrete melting point of about 142° C. Inone embodiment, the ethylenebisamide wax has a discrete melting point inthe range from about 120° C. to about 160° C. In one embodiment, theethylenebisamide wax has a discrete melting point in the range fromabout 130° C. to about 150° C. In one embodiment, the ethylenebisamidewax has a discrete melting point of about 140° C.

In one embodiment, the ethylenebisstearamide is ACRAWAX® C, availablefrom LONZA, Inc. ACRAWAX® C. has a discrete melt temperature of 142° C.

In other embodiments of the binder composition, other ethylenebisamidesinclude the bisamides formed from the fatty acids ranging from C₁₂ toC₃₀. Illustrative of these acids are lauric acid, palmitic acid, oleicacid, linoleic acid, linolenic acid, oleostearic acid, stearic acid,myristic acid, and undecalinic acid. Unsaturated forms of these fattyacids may also be used.

Additives

DEBINDING ACCELERATORS

In one embodiment, the binder composition comprises a polycarbonatepolymer; an ethylenebisamide wax; a guanidine wetting agent; and anadditive which in use accelerates debinding of the binder composition.In one embodiment, the debinding accelerator is a generator of freeradicals, such as a peroxide or an azo compound. The free radicalgenerated by the free radical generator attacks the polycarbonatepolymer chain, scissioning the chain in the process referred to hereinas chain scission.

In one embodiment, the debinding accelerator is an organic peroxide. Inone embodiment, the debinding accelerator is an azo compound.

In one embodiment, the debinding accelerator is a dialkyl peroxide. Inone embodiment, the debinding accelerator is a symmetrical dialkylperoxide. In one embodiment, the debinding accelerator is anon-symmetrical dialkyl peroxide. In one embodiment, the alkyl group issubstituted with one or more of a halogen, a nitro-group, a hydroxylgroup, an amine group, an amide group, a carbonyl group, a carboxylgroup, or an anhydride group. In one embodiment, the debindingaccelerator is an organic hydroperoxide. In one embodiment, thedebinding accelerator is a diaryl peroxide. In one embodiment, thedebinding accelerator is a symmetrical diaryl peroxide. In oneembodiment, the debinding accelerator is a non-symmetrical diarylperoxide. In one embodiment, the aryl group is substituted with one ormore of a halogen, a nitro-group, a hydroxyl group, an amine group, anamide group, a carbonyl group, a carboxyl group, or an anhydride group.In one embodiment, the organic peroxide is an arylalkyl peroxide, i.e.,a peroxide such as t-butyl benzyl peroxide. In such an embodiment,either or both of the alkyl group or the aryl group may be substitutedas disclosed above for dialkyl and diaryl peroxides.

Suitable organic peroxides for the debinding accelerator embodiment ofthe additive of the present invention include at least one of thefollowing: dicumyl peroxide, di-t-butylperoxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-amylperoxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,α,α′-di(t-butylperoxy)diisopropylbenzene, decanoyl peroxide, lauroylperoxide, succinic peroxide, 2-dihydroperoxybutane and multimersthereof, 2,4-pentanedione peroxide, di(n-propyl)peroxydicarbonate,di(sec-butyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate,1,1-dimethyl-3-hydroxybutyl peroxyneodecanoate, α-cumylperoxyneodecanoate, 1,1-dimethyl-3-hydroxybutyl peroxyneoheptanoate,α-cumyl peroxyneoheptanoate, t-amyl peroxyneodecanoate,t-butylperoxyneodecanoate, t-amyl peroxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy)hexane,t-amylperoxy-2-ethylhexanoate, t-butyl peroxyacetate, t-amylperoxyacetate, t-butyl perbenzoate, t-amyl perbenzoate,O,O-t-amyl-O-(2-ethylhexyl)monoperoxycarbonate,di-t-butyldiperoxyphthalate, t-butylcumylperoxide,O,O-t-butyl-O-(isopropyl)monoperoxycarbonate,2,5-dimethyl-2,5-di(benzoylperoxy)hexane,O,O-t-butyl-1-(2-ethylhexyl)monoperoxycarbonate, cumene hydroperoxide,t-butyl hydroperoxide, t-amyl hydroperoxide,1,1-di(t-butylperoxy)-3,3,5-trimethyl-cyclohexane,1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)cyclohexane,ethyl-3,3-di(t-butylperoxy)butyrate, andethyl-3,3-di(t-amylperoxy)butyrate,1,3-bis(t-butylperoxyisopropyl)benzene, 1,1-bis(t-butylperoxy)valerate,benzoyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoylperoxide, 3,5,5-trimethylhexanoyl peroxide, 2,4-dichlorobenzoylperoxide, m-toluyl peroxide, methylethylketone peroxide, cyclohexanoneperoxide, 3,5,5-trimethylhexanone peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylhexane, 1,1-bis(t-butylperoxy)-cyclohexane, 2,2-bis(t-butyl peroxy)octane,diisopropylbenzenehydro peroxide, diisopropyl peroxydicarbonate,t-butylperoxy-2-ethylhexanoate, t-butyl peroxy neodecanate, t-butylperoxy laurate, t-butyl peroxy isopropylcarbonate,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,2′-bis(t-butylperoxy)-diisopropylbenzene,4,4,′-bis(t-butylperoxy)butylvalerate, t-butylperterephthalate,2,2-di-(t-butylperoxy)butane, n-butyl 4,4′-di-t-butylperoxyvalerate,2,4-dichlorobenzoyl peroxide, o-chlorobenzoyl peroxide,t-butylperoxyneohexanoate, di-(3-methoxybutyl)peroxydicarbonate,4,4′-dichloro benzoyl peroxide, tert-butylperoxymaleic acid,2,4-pentanedione peroxide and2,5-dimethyl2,5-di(2-ethylhexanoylperoxy)hexane. Other aromaticperoxides may be used, such as anthracene peroxide and naphthaleneperoxide. The foregoing list is intended to be exemplary, and suitableperoxides not included here may be selected by those of skill in the artbased on similarities to the foregoing list. In particular, for example,it is noted that any of the foregoing peroxides may be substituted byany of the substituents identified above.

In one preferred embodiment, the organic peroxide is2,5-dimethyl-2,5-di(t-butylperoxy)hexane. In one embodiment, the organicperoxide is benzoyl peroxide. In one embodiment, the organic peroxide isperoxy benzoic acid.

In general, the preferred organic peroxides are described by the generalformulas R₁₀—O—O—R₁₁ or R₁₀—O—O—R₁₁—O—O—R₁₂ wherein R₁₀, R₁₁ and R₁₂ areeach independently alkyl, aryl, substituted alkyl or substituted aryl.

Particularly preferred organic peroxides are dialkyl peroxides where theterm alkyl radical is defined as a conventional saturated straight-chainor branched lower alkyl radical having up to six carbon atoms.

Many of the foregoing peroxides are liquids at room temperature, or havea relatively low melting point. In such cases, it has been foundadvisable and helpful to place, or adsorb, the peroxides on a solidcarrier. Such solid carriers may be one or more of a polyolefin, a clay,calcium carbonate or silica, or similar known carrier materials. Whenthey are absorbed on such carriers, the weight percentage of organicperoxide ranges specified above do not include the particulate carrier.In one embodiment, the solid carrier is a relatively low molecularweight polymer such as polypropylene or polyethylene. Since theperoxides are intended to assist in and accelerate debinding of thepolycarbonate polymer component of the binder composition, the molecularweight preferably is such that the solid carrier decomposes at atemperature somewhat above 180° C., the temperature of debinding of thepolycarbonate component. An organic, ash-free solid carrier ispreferred, since such a carrier will decompose to produce the sameinnocuous, gaseous products (CO₂ and H₂O) as produced by thepolycarbonate.

In one embodiment, the solid carrier material upon which the debindingaccelerator is adsorbed is an inorganic material such as calciumcarbonate or silica. In such embodiments, while it may appearundesirable to include materials such as calcium or silicon which willnot debind into gaseous or liquid products, the amounts of carrier arerelatively small, and in most cases do not appreciably affect thequality of the parts so produced. In cases where even a trace of suchmaterials is undesirable or prohibited, other, higher-melting organicperoxides may be suitably selected, which are not liquids and do notneed a solid carrier, or the solid carrier selected may be a polymerwhich does decompose to CO₂ and H₂O.

In one embodiment, the free radical source may be an inorganic peroxide.In one embodiment, the inorganic peroxide is one which decomposes toyield products which do not produce ash. In one embodiment, theinorganic peroxide is ammonium peroxysulfate ((NH₄)₂S ₂O₈). In oneembodiment, the inorganic peroxide is a volatile peroxysulfate. Avolatile peroxysulfate is one which decomposes to yield ash-free orlow-ash products. In one embodiment, the inorganic peroxide is avolatile peroxynitrate. A volatile peroxynitrate is one which decomposesto yield ash-free or low-ash products. In one embodiment, the inorganicperoxide is urea peroxide. In one embodiment, the inorganic peroxide ishydrogen peroxide.

In another embodiment, the free radical source utilized as the debindingaccelerator may be an azo compound. Suitable azo compounds include, forexample: 2,2′-azobisisobutyronitrile,2,2′-azobis-2,4-dimethylvaleronitrile, 4,4-azobis-4-cyano valeric acid,1-azobis-1-cyclohexane carbonitrile, dimethylazoisobutyronitrile anddimethyl-2,2′-azobis-isobutylate. Other similar, known azo compounds maybe suitably selected. Further examples include:2,2′-azobis(2-methylbutanenitrile) and1,1′-azobis(cyclohexanecarbonitrile).

In addition, in other embodiments the debinding accelerator may be anysource of free radicals which can scission the poly(propylene)carbonatepolymer chain. Thus, for example, treating the green composition withozone or radiation such as gamma rays, electron sources such as electronguns, electric arc and plasmas. The debinding accelerator need onlyprovide a free electron which can scission the polymer chain intosmaller polymers, as described above.

As discussed above, the debinding accelerator increases the rate atwhich the polycarbonate debinds during debinding of the bindercomposition. Thus, the debinding accelerator is believed to cleave thepolycarbonate polymer into polymeric fragments.

DEBINDING EXTENDER

In one embodiment, the present invention relates to a binder compositioncomprising: a polycarbonate polymer; an ethylenebisamide wax; aguanidine wetting agent; and an additive which extends debinding of thebinder composition. In one embodiment, the additive is a debindingextender which extends debinding to higher temperatures and/or longerdebind times.

In one embodiment, the debinding extender is a polymer having adebinding temperature in the range from about 450° C. to about 850° C.In one embodiment, the debinding extender is a polymer having adebinding temperature in the range from about 500° C. to about 750° C.In one embodiment, the debinding extender is a polymer having adebinding temperature in the range from about 475° C. to about 700° C.In one embodiment, the debinding extender is a polymer having adebinding temperature in the range from about 450° C. to about 750° C.In one embodiment, the debinding extender is a polymer having a debindtemperature greater than the debind temperature of the guanidine wettingagent with which the debinding extender is combined in the debindingcomposition.

While the debinding extender may be any polymer having a suitabledebinding temperature and debinding by decomposing into simple, safemolecules, certain debinding extenders are preferred. In one embodiment,the debinding extender is at least one of a polypropylene polymer or apolymethacrylate polymer. The debinding extender may be a suitableacrylate polymer. When the debinding extender is a polypropylenepolymer, in one embodiment, the debinding extender is an atacticpolypropylene. In another embodiment it is a syntactic polypropylene. Inanother embodiment, the debinding extender is isotactic polypropylene.In one embodiment, the debinding extender is a mixture of two or allthree of atactic, syntactic and isotactic polypropylene.

In one embodiment, the debinding extender is a polypropylene polymeravailable under the trade name ProFlow 3000 from Polyvisions, Inc.,York, Pa.

In one embodiment, the debinding extender is a polymethacrylate polymer.In another embodiment, the debinding extender is apoly-alkylmethacrylate polymer. The alkyl substituent may be a C₁-C₁₀alkyl group. In one embodiment, the debinding extender is apolymethylmethacrylate polymer (PMMA).

In one embodiment, the debinding extender is a polymer having a weightaverage molecular weight in the range from about 25,000 to about250,000. In one embodiment, the polymer has a weight average molecularweight in the range from about 40,000 to about 120,000. In oneembodiment, the debinding extender is a polypropylene polymer which hasa weight average molecular weight of about 50,000. In one embodiment,the debinding extender is a polymethacrylate polymer which has a weightaverage molecular weight of about 100,000.

In another embodiment, the debinding extender is a polyethylene polymer.In another embodiment, the debinding extender is a polyacrylate polymer.Additional polymers which may be suitable as the debinding extenderinclude polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral,polypropenal, polyacetal and polystyrene.

Quantities of Components in the Binder and Green Compositions

It is a practice in the art of powder metal to refer to a bindercomposition in terms of parts by weight, or percent of each component ona weight basis, and to refer to a green composition in terms of parts byvolume, or percent of each component on a volume bases. Thus, the amountof each component in the binder composition is expressed as weightpercent, or wt %. The amounts of the inorganic powder and the bindercomposition combined to form the green composition are expressed asvolume percent, or vol %. This practice is followed throughout thepresent specification and claims.

In one embodiment, the binder composition comprises the guanidinewetting agent in the range from about 5 wt % to about 30 wt % based onthe binder composition, the polycarbonate polymer in the range fromabout 30 wt % to about 85 wt % based on the binder composition, and theethylenebisamide wax in the range from about 10 wt % to about 40 wt %based on the binder composition. In one embodiment of the bindercomposition, the guanidine wetting agent is present at about 15.5 wt %,the polycarbonate polymer is present at about 59.4 wt %, andethylenebisstearamide is present at about 25.1 wt %, each weight percentbased on the binder composition. In one embodiment, the polycarbonatepolymer is Q-PAC™ 40 brand of poly(propylene carbonate), and is presentat about 60 wt %. In one embodiment, the ethylenebisamide is ACRAWAX® Cbrand of ethylenebisstearamide, and is present at about 25 wt %.

In one embodiment, the binder composition comprises the guanidinewetting agent in the range from about 10 wt % to about 25 wt % based onthe binder composition, the polycarbonate polymer in the range fromabout 40 wt % to about 60 wt % based on the binder composition, and theethylenebisamide wax in the range from about 15 wt % to about 35 wt %based on the binder composition.

In one embodiment, when the additive is an debinding accelerator, thedebinding accelerator is present in the range from about 0.01 wt % toabout 10 wt % of the binder composition. In one embodiment, when theadditive is an debinding accelerator, the debinding accelerator ispresent in the range from about 2.6 wt % to about 2.9 wt % of the bindercomposition. In one embodiment, when the additive is an debindingaccelerator, the debinding accelerator is present in the range fromabout 1.3 wt % to about 1.5 wt % of the binder composition.

In one embodiment, when the additive is a debinding extender, thedebinding extender is present in the range from about 1 wt % to about 20wt % of the binder composition. In one embodiment, when the additive isa debinding extender, the debinding extender is present in the rangefrom about 6 wt % to about 8 wt % of the binder composition. In oneembodiment, when the additive is a debinding extender, the debindingextender is present in the range from about 14 wt % to about 16 wt % ofthe binder composition.

The binder composition of the present invention may also be used for P&Sapplications. In such applications, the binder composition comprises theguanidine wetting agent in the range from about 5 wt % to about 30 wt %based on the binder composition, the polycarbonate polymer in the rangefrom about 10 wt % to about 50 wt % based on the binder composition, andthe ethylenebisamide wax in the range from about 30 wt % to about 70 wt% based on the binder composition.

In one embodiment, when the additive is an debinding accelerator in aP&S application, the debinding accelerator is present in the range fromabout 0.01 wt % to about 10 wt % of the binder composition. In oneembodiment, when the additive is an debinding accelerator, the debindingaccelerator is present in the range from about 2.8 wt % to about 3.2 wt% of the binder composition. In one embodiment, when the additive is andebinding accelerator, the debinding accelerator is present in the rangefrom about 1.4 wt % to about 1.6 wt % of the binder composition.

In one embodiment, when the additive is a debinding extender in a P&Sapplication, the debinding extender is present in the range from about 1wt % to about 20 wt % of the binder composition. In one embodiment, whenthe additive is a debinding extender, the debinding extender is presentin the range from about 7 wt % to about 9 wt % of the bindercomposition. In one embodiment, when the additive is a debindingextender, the debinding extender is present in the range from about 15wt % to about 18 wt % of the binder composition.

The binder composition of the present invention is designed to becombined with an inorganic powder, to form a green composition for usein PIM or P&S. For PIM, in one embodiment, the green compositionincludes the binder composition, as described above, and at least oneinorganic powder selected from a metal powder, a metal oxide powder, anon-metallic powder and a ceramic powder. In one embodiment, the greencomposition includes the binder composition in an amount in the rangefrom about 30 vol % to about 60 vol % and the inorganic powder orpowders in an amount from about 70 vol % to about 40 vol %. In oneembodiment, the green composition includes the binder composition in anamount in the range from about 40 vol % to about 50 vol % and theinorganic powder is present in an amount from about 60 vol % to about 50vol %. In one embodiment, the green composition includes the bindercomposition in an amount of about 35 vol % and the inorganic powder inan amount of about 65 vol %.

The binder composition of the present invention is also suitable for usewith an inorganic powder, to form a green composition for use in P&S. Inone embodiment, the green composition includes the binder composition,as described above, and at least one inorganic powder selected from ametal powder, a metal oxide powder, a non-metallic powder and a ceramicpowder. In one embodiment, the green composition includes the bindercomposition in an amount in the range from about 1 vol % to about 10 vol% and the inorganic powder or powders in an amount from about 99 vol %to about 90 vol %. In one embodiment, the green composition includes thebinder composition in an amount in the range from about 2 vol % to about5 vol % and the inorganic powder is present in an amount from about 98vol % to about 95 vol %. In one embodiment, the green compositionincludes the binder composition in an amount of about 2.5 vol % and theinorganic powder in an amount of about 97.5 vol %.

Inorganic Powders

Inorganic powders used in the present invention include metallic, metaloxide, intermetallic and/or ceramic powders. The powders may be oxidesor chalcogenides of metallic or non-metallic elements. An example ofmetallic elements which may be present in the inorganic powders includecalcium, magnesium, barium, scandium, titanium, vanadium, chromium,manganese, iron, cobalt, nickel, copper, zinc, yttrium, niobium,molybdenum, ruthenium, rhodium, silver, cadmium, lanthanum, actinium,gold or combinations of two or more thereof. In one embodiment, theinorganic powder may contain rare earth or ferromagnetic elements. Therare earth elements include the lanthanide elements having atomicnumbers from 57 to 71, inclusive and the element yttrium, atomic number39.

Ferromagnetic metals, for purposes of this invention, include iron,nickel, cobalt and numerous alloys containing one or more of thesemetals. In another embodiment, the metals are present as alloys of twoor more of the aforementioned elements. In particular, prealloyedpowders such as low alloy steel, bronze, brass and stainless steel aswell as nickel-cobalt based super alloys may be used as inorganicpowders.

The inorganic powders may comprise inorganic compounds of one or more ofthe above-described metals. The inorganic compounds include ferrites,titanates, nitrides, carbides, borides, fluorides, sulfides, hydroxidesand oxides of the above elements. Specific examples of the oxide powdersinclude, in addition to the oxides of the above-identified metals,compounds such as beryllium oxide, magnesium oxide, calcium oxide,strontium oxide, barium oxide, lanthanum oxide, gallium oxide, indiumoxide, selenium oxide, zinc oxide, aluminum oxide, silica, zirconia,mullite, mica, indium tin oxide, rare earth oxides, titania, yttria,etc. Specific examples of oxides containing more than one metal,generally called double oxides, include perovskite-type oxides such asNaNbO₃, SrZrO₃, PbZrO₃, SrTiO₃, BaZrO₃, BaTiO₃; spinel-type oxides suchas MgAl₂O₄, ZnA₂O₄, CoAl₂O₄, NiAl₂O₄, NiCr₂O₄, FeCr₂O₄, MgFe₂O₄,ZnFe₂O₄, etc.; illmenite-types oxides such as MgTiO₃ MnTiO₃, FeTiO₃,CoTiO₃, ZnTiO₃, LiTaO₃, etc.; and garnet-type oxides such as Gd₃Ga₅O₁₂and rare earth-iron garnet represented by Y₃Fe₅O₁₂. The inorganic powdermay also be a clay. Examples of clays include kaolinite, nacrite,dickite, montmorillonite, montronite, spaponite, hectorite, etc.

An example of non-oxide powders include carbides, nitrides, borides andsulfides of the metals described above. Specific examples of thecarbides include SiC, TiC, WC, TaC, HfC, ZrC, AlC; examples of nitridesinclude Si₃N₄, AIN, BN and Ti₃N₄; and borides include TiB₂, ZrB₂, B₄Cand LaB₆. In one embodiment, the inorganic powder is silicon nitride,silicon carbide, zirconia, alumina, aluminum nitride, barium ferrite,barium-strontium ferrite or copper oxide. In another embodiment, thepowder is a semiconductor, for example, GaAs, Si, Ge, Sn, AlAs, AlSb,GaP, GaSb, InP, InAs, InSb, CdTe, HgTe, PbSe, PbTe, and any of the manyother known semiconductors. In another embodiment, the inorganic powderis alumina or clay.

Acids for Reaction with Guanidine

The acidic compounds useful in making the reaction product of guanidineand an acid of the present invention include carboxylic acids, sulfonicacids, phosphorus acids, phenols or mixtures of two or more thereof.Preferably, the acidic organic compounds are carboxylic acids orsulfonic acids. The carboxylic and sulfonic acids may have substituentgroups derived from the above described polyalkenes. Selection criteriafor the appropriate acid are provided above, based on the surface chargeand isoelectric point of the inorganic powder used in preparing thegreen composition.

The carboxylic acids may be aliphatic or aromatic, mono- orpolycarboxylic acid or acid-producing compounds. The acid-producingcompounds include anhydrides, lower alkyl esters, acyl halides, lactonesand mixtures thereof unless otherwise specifically stated.

Illustrative fatty carboxylic acids include palmitic acid, stearic acid,myristic acid, oleic acid, linoleic acid, behenic acid,hexatriacontanoic acid, tetrapropylenyl-substituted glutaric acid,polybutenyl (Mn=200-1,500, preferably 300-1,000)-substituted succinicacid, polypropylenyl, (Mn=200-1,000, preferably 300-900)-substitutedsuccinic acid, octadecyl-substituted adipic acid, 9-methylstearic acid,stearyl-benzoic acid, eicosane-substituted naphthoic acid,dilauryl-decahydronaphthalene carboxylic acid, mixtures of these acids,and/or their anhydrides. Aliphatic fatty acids include the saturated andunsaturated higher fatty acids containing from about 12 to about 30carbon atoms. Illustrative of these acids are lauric acid, palmiticacid, oleic acid, linoleic acid, linolenic acid, oleostearic acid,stearic acid, myristic acid, and undecalinic acid, alpha-chlorostearicacid, and alphanitrolauric acid. Branched fatty acids, both saturatedand unsaturated, in the range from about 6 to about 25 carbon atoms areincluded. Such branched fatty acids include versatic acids, availablefrom Shell Chemicals. For example, Shell Chemical produces a versaticacid known as Monomer Acid, which is the distilled product obtainedduring the manufacture of tall oil-based dimer acid. Monomer Acid is amixture of both branched and straight-chain predominantly C₁₈ mono fattyacids. One example is Versatic 10, a synthetic saturated monocarboxylicacid of highly branched structure containing ten carbon atoms. Itsstructure may be represented as:

where R1, R2 and R3 are alkyl groups at least one of which is alwaysmethyl.

The sulfonic acids useful in making the guanidine wetting agents includethe sulfonic and thiosulfonic acids. Generally they are salts ofsulfonic acids. The sulfonic acids include the mono- or polynucleararomatic or cycloaliphatic compounds. The oil-soluble sulfonates can berepresented for the most part by one of the following formulae:R⁷—T—(SO₃)_(d) and R⁸—(SO₃)_(e), wherein T is a cyclic nucleus such as,for example, benzene, naphthalene, anthracene, diphenylene oxide,diphenylene sulfide, petroleum naphthenes, etc.; R⁷ is an aliphaticgroup such as alkyl, alkenyl, alkoxy, alkoxyalkyl, etc.; (R⁷)+T containsa total of at least about 15 carbon atoms; R⁸ is an aliphatichydrocarbyl group containing at least about 15 carbon atoms and d and eare each independently an integer from 1 to about 3, preferably 1.Examples of R⁸ are alkyl, alkenyl, alkoxyalkyl, carboalkoxyalkyl, etc.Specific examples of R⁸ are groups derived from petrolatum, saturatedand unsaturated paraffin wax, and the above-described polyalkenes. Thegroups T, R⁷, and R⁸ in the above formulae can also contain otherinorganic or organic substituents in addition to those enumerated abovesuch as, for example, hydroxy, mercapto, halogen, nitro, amino, nitroso,sulfide, disulfide, etc. In the above Formulae, d and e are at least 1.

Illustrative examples of these sulfonic acids includemonoeicosane-substituted naphthalene sulfonic acids, dodecylbenzenesulfonic acids, didodecylbenzene sulfonic acids, dinonylbenzene sulfonicacids, cetylchlorobenzene sulfonic acids, dilauryl beta-naphthalenesulfonic acids, the sulfonic acid derived by the treatment ofpolybutenyl, having a number average molecular weight (Mn) in the rangeof about 500, preferably about 800 to about 5000, preferably about 2000,more preferably about 1500, with chlorosulfonic acid, nitronaphthalenesulfonic acid, paraffin wax sulfonic acid, cetyl-cyclopentane, sulfonicacid, lauryl-cyclohexane sulfonic acids, polyethylenyl (Mn=300-1,000,preferably 750) sulfonic acids, etc. Normally the aliphatic groups willbe alkyl and/or alkenyl groups such that the total number of aliphaticcarbons is at least about 8, preferably at least 12.

A preferred group of sulfonic acids are mono-, di-, and tri-alkylatedbenzene and naphthalene (including hydrogenated forms thereof) sulfonicacids. Illustrative of synthetically produced alkylated benzene andnaphthalene sulfonic acids are those containing alkyl substituentshaving from about 8 to about 30 carbon atoms, preferably about 12 toabout 30 carbon atoms, and advantageously about 24 carbon atoms. Suchacids include di-isododecyl-benzene sulfonic acid,polybutenyl-substituted sulfonic acid, polypropylenyl-substitutedsulfonic acids of Mn=300-1000, preferably 500-700, cetylchlorobenzenesulfonic acid, di-cetyinaphthalene sulfonic acid, di-lauryldiphenylethersulfonic acid, diisononylbenzene sulfonic acid, di-isooctadecylbenzenesulfonic acid, stearyinaphthalene sulfonic acid, and the like.

The production of sulfonates from detergent manufactured by-products byreaction with, e.g., SO₃, is well known to those skilled in the art.See, for example, the article “Sulfonates” in Kirk-Othmer “Encyclopediaof Chemical Technology”, Second Edition, Vol. 19, pp. 291 et seq.published by John Wiley & Sons, New York (1969).

The phosphorus-containing acids useful in making the guanidine wettingagents include any phosphorus acids such as phosphoric acid or esters;and thiophosphorus acids or esters, including mono and dithiophosphorusacids or esters. Preferably, the phosphorus acids or esters contain atleast one, preferably two, hydrocarbyl groups containing from 1 to about50 carbon atoms, typically 1, preferably 3, more preferably about 4 toabout 30, preferably to about 18, more preferably to about 8.

In one embodiment, the phosphorus-containing acids are dithiophosphoricacids which are readily obtainable by the reaction of phosphoruspentasulfide (P₂S₅) and an alcohol or a phenol. The reaction involvesmixing at a temperature of about 20° C. to about 200° C. four moles ofalcohol or a phenol with one mole of phosphorus pentasulfide. Hydrogensulfide is liberated in this reaction. The oxygen-containing analogs ofthese acids are conveniently prepared by treating the dithioic acid withwater or steam which, in effect, replaces one or both of the sulfuratoms with oxygen.

In one embodiment, the phosphorus-containing acid is the reactionproduct of the above polyalkenes and phosphorus sulfide. Usefulphosphorus sulfide-containing sources include phosphorus pentasulfide,phosphorus sesquisulfide, phosphorus heptasulfide and the like.

The reaction of the polyalkene and the phosphorus sulfide generally mayoccur by simply mixing the two at a temperature above 80° C., preferablybetween 100° C. and 300° C. Generally, the products have a phosphoruscontent from about 0.05% to about 10%, preferably from about 0.1% toabout 5%. The relative proportions of the phosphorus sulfide to theolefin polymer is generally from 0.1 part to 50 parts of the phosphorussulfide per 100 parts of the olefin polymer.

The phenols useful in making the guanidine wetting agents may berepresented by the formula (R)_(f)—Ar—(OH)_(g), wherein R and Ar aredefined above; f and g are independently numbers of at least one, thesum of f and g being in the range of two up to the number ofdisplaceable hydrogens on the aromatic nucleus or nuclei of Ar.Preferably, f and g are independently numbers in the range of 1 to about4, more preferably 1 to about 2. R and f are preferably such that thereis an average of at least about 8 aliphatic carbon atoms provided by theR groups for each phenol compound. Examples of phenols includeoctylphenol, nonylphenol, propylene tetramer substituted phenol,tri(butene)-substituted phenol, polybutenyl-substituted phenol andpolypropenyl-substituted phenol.

Other Additives

Other additives used in prior art binder compositions are not necessarywith the binder composition of the present invention. In one embodiment,no additives beyond the inventive binder composition are used. In oneembodiment, as deemed necessary, small amounts of other materials may beadded to the composition of the present invention. For example,plasticizers may be added to the compositions to provide more workablecompositions. Examples of plasticizers normally utilized in inorganicformulations include dioctyl phthalate, dibutyl phthalate, benzyl butylphthalate and phosphate esters.

Methods

The present invention further relates to a method for forming a part bypowder injection molding, comprising the steps of (a) forming a greencomposition comprising a binder composition and an inorganic powder,wherein the binder composition comprises a polycarbonate polymer, anethylenebisamide wax, a guanidine wetting agent, and an additive and (b)heating the green composition to debind the green composition, whereinthe additive accelerates or extends debinding step (b). In oneembodiment, step (b) results in reverse debinding of the bindercomposition. In one embodiment, the inorganic powder is selected from ametal powder, a metal oxide powder, an intermetallic powder and aceramic powder.

In one embodiment, the additive is an debinding accelerator whichaccelerates debinding step (b) as described above. In one embodiment,the debinding accelerator is an organic peroxide as described above. Inone embodiment, the organic peroxide is a dialkyl peroxide as describedabove.

In one embodiment, the additive is a debinding extender which extendsdebinding step (b). In one embodiment, the debinding extender is apolymer having a debinding temperature in the range from about 450° C.to about 850° C. as described above. In one embodiment, the debindingextender is at least one of a polypropylene polymer or apolymethacrylate polymer as described above. In one embodiment, thedebinding extender is a polypropylene polymer having a weight averagemolecular weight of about 50,000 as described above. In one embodiment,the debinding extender is a polymethacrylate polymer having a weightaverage molecular weight of about 100,000 as described above.

In one embodiment, the debinding step (b) includes a plurality oftemperature increases to elevated temperatures, and each of the elevatedtemperatures is maintained substantially constant for a period of time.In one embodiment, a first elevated temperature corresponds to thedebinding temperature of the polycarbonate polymer, a second elevatedtemperature corresponds to the debinding temperature of theethylenebisamide wax, and a third elevated temperature corresponds tothe debinding temperature of the guanidine wetting agent.

In one embodiment, the additive reduces the time for debinding of thepolycarbonate polymer.

In one embodiment, the additive debinds at a fourth elevatedtemperature, the fourth elevated temperature being higher than saidfirst, second and third elevated temperatures, thus extending thedebinding.

In one embodiment, the method further comprises a step of transferringthe flowable green composition into a mold for a part.

In one embodiment, the debinding step (b) comprises heating the part toa temperature at which the binder composition debinds. In oneembodiment, the method further comprises a step of heating the part to atemperature at which the powder is sintered. In one embodiment, thedebinding step (b) results in reverse debinding of the bindercomposition.

In one embodiment, the debinding step (b) comprises heating the greencomposition to a plurality of elevated temperatures to debind the greencomposition by reverse debinding, wherein a first elevated temperaturecorresponds to the debinding temperature of the polycarbonate polymer, asecond elevated temperature corresponds to the debinding temperature ofthe ethylenebisamide wax, and a third elevated temperature correspondsto the debinding temperature of the guanidine wetting agent.

In one embodiment, the additive is a debinding extender and step (b)further comprises heating to a fourth elevated temperature whichcorresponds to the debinding temperature of the debinding extender,thereby extending the debinding.

In another embodiment, the method comprises steps of transferring thegreen composition into a mold for a part, heating the part to atemperature at which the binder composition debinds, further heating thepart to a temperature at which the powder is sintered to form the part,and then cooling and removing the part from the mold. In anotherembodiment, the transferring step includes heating and injection of thegreen composition into a mold for powder injection molding. In anotherembodiment, the transferring step includes gravity feeding the greencomposition into a mold for press & sinter molding. In anotherembodiment of the method, the heating step is performed as a series oftemperature increases to selected temperatures, in which the selectedtemperatures correspond to debinding temperatures of the components inthe binder composition. In another embodiment, the selected temperaturesare held for a period of time, to allow the component to be deboundprior to increasing the temperature to a debinding temperature ofanother component. In one embodiment of the method, the order ofdebinding is polycarbonate polymer first, ethylenebisamide second,guanidine wetting agent third. In one embodiment, the additive is adebinding extender which completes debinding subsequent to thecompletion of debinding of the guanidine wetting agent. In oneembodiment, a wicking agent may be used in the debinding step. Inanother embodiment, the wicking agent may be used in both the debindingstep and the sintering step. The wicking agent may be, for example, afine alumina or zirconia sand.

In one embodiment of the method, the guanidine wetting agent is areaction product of guanidine and an acid selected from organic acid, afatty acid and a stronger acid such as an alkyl sulfonic acid. In oneembodiment of the method, the guanidine wetting agent is guanidinestearate. In one embodiment of the method, the guanidine wetting agentis guanidine ethyl hexanoate. In one embodiment of the method, theguanidine wetting agent is guanidine lauryl sulfonate.

In one embodiment of the method, the polycarbonate polymer has a numberaverage molecular weight in the range from about 25,000 to about 50,000.In one embodiment of the method, the polycarbonate polymer has a numberaverage molecular weight in the range from about 30,000 to about 45,000.In one embodiment of the method, the polycarbonate polymer has a numberaverage molecular weight in the range from about 35,000 to about 40,000.

In one embodiment of the method, the ethylenebisamide wax has a discretemelting point in the range from about 120° C. to about 160° C. In oneembodiment of the method, the ethylenebisamide wax has a discretemelting point in the range from about 130° C. to about 150° C. In oneembodiment of the method, the ethylenebisamide wax has a discretemelting point of about 140° C. In one embodiment of the method, theethylenebisamide is ACRAWAX C® brand of ethylenbisstearamide and has adiscrete melting point of about 142° C.

In one embodiment of the method, the additive is an debindingaccelerator, which is an organic peroxide. In another embodiment, thedebinding accelerator is an azo compound. In another embodiment, thedebinding accelerator is an externally applied free radical source. Inthe embodiments of the method, the debinding accelerator may be any ofthe debinding accelerators identified and described hereinabove.

In one embodiment of the method, the additive is a debinding extenderwhich is a polymer. In another embodiment, the debinding extender is apolypropylene polymer. In another embodiment, the debinding extender isa polymethacrylate polymer. In the embodiments of the method, thedebinding extender may be any of the debinding extenders identified anddescribed hereinabove.

In one embodiment, the method employs both an debinding accelerator anda debinding extender. In such an embodiment, since the inorganic powderis a higher-temperature-sintering material, the debinding extender isneeded to assure that the binder composition continues to bind theinorganic powder particles in place until the onset or initiation ofsintering. For the same reason, the initial heating steps which debindthe polycarbonate polymer likely do not occur together with anypre-sintering, so, once the green composition has been placed in themold, the low-temperature-sintering components such as the polycarbonatepolymer, can be expeditiously debound. For this purpose, the debindingaccelerator may be added.

In one embodiment of the method, the binder composition comprises theguanidine wetting agent in the range from about 5 wt % to about 30 wt %based on the binder composition, the polycarbonate polymer in the rangefrom about 30 wt % to about 85 wt % based on the binder composition, andthe ethylenebisamide wax in the range from about 10 wt % to about 40 wt% based on the binder composition. In one embodiment of the method, thebinder composition comprises the guanidine wetting agent at about 15.5wt %, the polycarbonate polymer at about 59.4 wt %, and ethylenebisamideat about 25.1 wt %, each weight percent based on the binder composition.In one embodiment of the method, the polycarbonate polymer is Q-PAC™ 40brand of poly(propylene carbonate), and is present at about 60 wt %. Inone embodiment of the method, the ethylenebisamide is ACRAWAX® C brandof ethylenebisstearamide, and is present at about 25 wt %. In oneembodiment of the method, the additive is an debinding accelerator whichis present in the range from about 0.01 wt % to about 10 wt % of thebinder composition. In another embodiment of the method, the additive isa debinding extender which is present in the range from about 1 wt % toabout 20 wt % of the binder composition. In one embodiment, both thedebinding accelerator and the debinding extender are present, in theabove proportions.

In one embodiment of the method, the binder composition comprises theguanidine wetting agent in the range from about 10 wt % to about 25 wt %based on the binder composition, the polycarbonate polymer in the rangefrom about 40 wt % to about 60 wt % based on the binder composition, andthe ethylenebisamide wax in the range from about 15 wt % to about 35 wt% based on the binder composition.

When either or both types of the additive are present, the relativeweight percentage of the other three binder components may be adjustedaccordingly. In one embodiment, the relative proportions between theother three components remain the same, each being reducedproportionately. In one embodiment, when an debinding accelerator ispresent, the amount of polycarbonate is reduced by an equivalent amount.In one embodiment, when an debinding accelerator is present, the amountof polycarbonate remains the same, but the amounts of one or both of theother components are reduced proportionately.

In one embodiment, when the debinding extender is present, the amount ofguanidine wetting agent remains the same, but the amounts of one or bothof the other components are reduced proportionately.

In one embodiment of the method, the binder composition is present in anamount in the range from about 30 vol % to about 60 vol % of the greencomposition and the inorganic powder is present in an amount from about70 vol % to about 40 vol % of the green composition. In one embodimentof the method, the binder composition is present in an amount in therange from about 40 vol % to about 50 vol % of the green composition andthe inorganic powder is present in an amount from about 60 vol % toabout 40 vol % of the green composition. In one embodiment, the greencomposition includes the binder composition in an amount of about 35 vol% and the inorganic powder in an amount of about 65 vol %.

Preparation

FIG. 1 is a schematic diagram of the steps in a generalized process formaking a part by powder injection molding in accordance with the presentinvention. In a first step 10 an inorganic powder and a bindercomposition according to the present invention are obtained andcombined. In one embodiment, the step of preparing the bindercomposition includes steps of mixing, blending and dispersing thecomponents of the binder composition as needed to prepare a homogenous,or nearly homogenous, mixture of the components in the bindercomposition, in a powder form. In one embodiment, the binder compositionand the inorganic powder are first dry blended to produce a homogenousmix of dry materials. In one embodiment, the binder composition ismicronized to a size similar to that of the inorganic powder with whichit will be combined to form the green composition. In one embodiment,the binder composition is ground to a particle size in the range fromabout 10 μm to about 100 μm.

In an optional second step (not shown) the inorganic powder and thebinder composition are combined in a premixing of the green composition.The optional premixing step may include mixing in, e.g., a ball mill. Inthis optional step, additional components, if used, may be added andblended into the mixture as desired.

In a step 20 the components of the green composition are fed into a twinscrew compounding extruder. In the step 20, while passing through thetwin screw compounding extruder, the components of the green compositionare subjected to a high shear for effectively combining the inorganicpowder and binder composition. While the use of a twin screw extruder ispreferred, it is not necessary to the process of the invention that atwin screw extruder be used. The twin screw extruder provides areliable, consistent, suitably thorough mixing of the ingredients. Otherknown and available mixing methods may be employed to achieve the mixingof the components of the green composition. For example, suitablythorough mixing may be attained with a sigma blade mixer, a doubleplanetary mixer, a single screw mixer, a paddle compounder or a shearroll compounder.

In one embodiment, the output from the twin screw compounding extruderis a string of the green composition, which is then fed to a pelletizer.In one embodiment, the output from the twin screw compounding extruderis pelletized by a pelletizing apparatus directly attached to theextruder apparatus. Forming the green composition into pelletsfacilitates handling, both for immediate and for subsequent use. Themixing in the twin screw compounding extruder in the step 20 facilitatesblending the various green compositions as may be required forparticular applications. The mixing in the twin screw compoundingextruder in the step 20 combines, compounds and pelletizes the greencomposition. The pellets formed by the step 20 may be cooled and storedfor later use, or may be used immediately with or without cooling.

In one embodiment of the step 20 the binder composition is dry blendedwith the inorganic powder prior to feeding to the twin screw compoundingextruder, and the blended components of the green composition are fedinto the extruder together. In one embodiment, the binder compositionand inorganic powder components of the green composition are fedseparately into the twin screw compounding extruder. In one embodiment,the binder composition is fed into the twin screw compounding extruderat a first point, and the inorganic powder component is fed in at asecond point, downstream from the first point.

In one embodiment, the twin screw compounding extruder is a Leistritz 18mm co-rotating twin screw compounding extruder. In one embodiment, theLeistritz twin screw extruder has the design shown in FIG. 2. A furtherdescription of FIG. 2 is provided below. In one embodiment, the greencomposition exiting the twin screw compounding extruder emerges in theform of a string, passing onto a conveyor, which is subsequently cooledand then cut into pellets.

Referring again to FIG. 1, in an injection molding step 30, the pelletsof the green composition are heated, melted, mixed and injected into amold having the desired shape of the part of interest. The part formedat this stage is known as a green part or a compact for a part. In oneembodiment, the molten green composition is injected into the mold at apressure in the range from about 100 psi (about 7 Kg/cm²) to about 2000psi (about 140 Kg/cm²). In one embodiment, the molten green compositionis injected into the mold at a pressure of about 800 psi (about 56Kg/cm²). In the injection step 30, pellets having different greencompositions may be blended. Following the injection step 30, the greenpart is cooled and released from the mold.

In one embodiment, the pellets are fed into a hopper and thence into ahorizontal injection molding machine. In one embodiment, the injectionmolding machine is a standard injection molding machine used forinjection molding parts in known processes.

In one embodiment, the green part has a green strength in the range ofabout 800 psi (about 56 Kg/cm²) to about 12,000 psi (about 844 Kg/cm²).In one embodiment, the green part has a green strength in the range ofabout 2000 psi (about 140 Kg/cm²) to about 8000 psi (about 562 Kg/cm²).In one embodiment, the green part has a green strength in the range ofabout 4000 psi (about 281 Kg/cm²) to about 6000 psi (about 422 Kg/cm²).

The green part is then transferred to a debinding/sintering oven, inwhich one or more steps of debinding 40 are carried out. In oneembodiment, the debinding step 40 includes a plurality of temperatureincreases to elevated temperatures. In one embodiment of the debindingstep 40, each of the elevated temperatures are maintained constant for aperiod of time. In one embodiment of the debinding step 40, the elevatedtemperatures correspond to temperatures at which individual ingredientsof the binder composition are debound. In one embodiment of thedebinding step 40, a first elevated temperature corresponds to thedebinding temperature of the polycarbonate polymer, a second elevatedtemperature corresponds to the debinding temperature of theethylenebisamide wax, and a third elevated temperature corresponds tothe debinding temperature of the guanidine wetting agent. In oneembodiment of the debinding step 40, the third elevated temperature ishigher than the second elevated temperature, and the second elevatedtemperature is higher than the first elevated temperature.

In one embodiment, when the additive is present in the form of adebinding extender, the part is heated to a fourth elevated temperature,and may be held at that temperature for a period of time. The fourthelevated temperature corresponds to the debinding temperature of thedebinding extender. The fourth elevated temperature is higher than thethird elevated temperature. The fourth elevated temperature may be inthe range from about 450° C. to about 850° C.

Following the debinding step 40, the green part is subjected to a step50 of sintering. The sintering step 50 may be performed in the same ovenin which the debinding step 40 was performed, or the green part may bemoved to a separate sintering oven for the sintering step 50.

The variables for the debinding process conditions include selection ofthe identity, pressure and flow rate of the atmosphere in the debindingoven chamber, selection of the temperatures for each debinding step,selection of the rate of increase in temperature during the transitionfrom one debinding step to the next, and selection of the time eachdebinding temperature is held while a particular component is deboundfrom the green composition. Additional variables arise from the exactnature of both the components of the binder composition and theinorganic powder used in the green composition. The time period at whicha particular debinding temperature is held during a debinding process isknown as “soaking” the green composition at that temperature. The timeperiods for soaking, and the rate of temperature increase between thesoaking steps should be selected for a given binder composition and agiven green composition. A certain amount of trial and error may berequired to optimize the debinding conditions for a given bindercomposition and green composition. The following general principles maybe applied to make an initial selection of debinding conditions, but thenumber of variables make it likely that some testing will be required.

In selecting the environment for the debinding and sintering, thetemperatures selected for each step of the debinding are primarilyinfluenced by the melting and decomposition temperature of eachcomponent of the binder composition and by the atmosphere in thedebinding oven chamber. However, other factors may be involved as well.

Generally, the temperature at which a part is soaked for removal of eachcomponent during the debinding corresponds to the onset temperature ofits decomposition. In a debinding process, it is helpful if a componentmelts before decomposing, but the important step is the decomposition.If the component melts prior to decomposing, as has been describedherein for the poly(propylene carbonate) polymer, it is helpful to theoverall debinding process due to the relatively small expansion ofvolume in melting as compared to decomposing into gaseous products.Thus, for example, a component may have a certain melting point, such asethylenebisstearamide which has a melting point of 142° C., but itsdebinding via decomposition is carried out at temperatures in the rangefrom about 190° C. to about 225° C., depending on the atmosphere in thedebinding oven chamber.

The atmosphere in the debinding oven chamber determines the speed ofdebinding at a given temperature. Generally, at a given temperature, anatmosphere of hydrogen results in faster debinding than a vacuum (e.g.,4-12 hours for hydrogen vs. 6-18 hours for vacuum), and a vacuum resultsin faster debinding than an inert atmosphere, for example of argon ornitrogen (e.g., 6-18 hours for vacuum vs. 8-24 hours for an inert gasatmosphere). Alternatively, for a given time for a debinding step, usingan atmosphere of hydrogen allows the debinding step to be carried out ata lower temperature than the same debinding step carried out in avacuum, and a vacuum allows the same debinding step to be carried out ata lower temperature than it would be carried out when in an inert gasatmosphere. Thus, for example, a polycarbonate debinding step which maybe carried out by soaking for 60 minutes at 160° C. in a hydrogenatmosphere, would need to be carried out by soaking for 60 minutes atabout 190° C. in a nitrogen atmosphere. Alternatively, a polycarbonatedebinding step which may require soaking for 60 minutes at 160° C. in ahydrogen atmosphere, may require soaking for about 90 minutes at 160° C.in a nitrogen atmosphere. The examples provided below provide anindication of the temperatures and times which may be required fordebinding the binder compositions of the present invention. Suitableatmospheres include, e.g., air, nitrogen, hydrogen, oxygen, argon, andother inert gases.

The pressure and flow rate of the gases used in the debinding ovenchamber provide another variable which must be considered in designing adebinding profile. In a hydrogen atmosphere, the pressure is typicallyfrom about 10% to about 20% above atmospheric, and the hydrogen ispassed through a 2 ft³ (about 56.6 liter) chamber at the rate of about10 ft³/hr (CFH) (about 28 liter/hr) to about 50 CFH (about 140liter/hr). In one embodiment in the same chamber at the rate of about 12CFH (about 34 liter/hr). In one embodiment in the same chamber at therate of about 15 CFH (about 42 liter/hr). In one embodiment in the samechamber at the rate of about 25 CFH (about 70 liter/hr). The flow rateshould be sufficient to provide from about 0.5 to about 5 atmosphereexchanges per hour in the chamber. When an atmosphere other than air isused, it is normally provided at a super-atmospheric pressure in orderto avoid leakage ingress of air into the debinding oven chamber. In oneembodiment, the pressure in the debinding oven chamber is about 780torr. Sub-atmospheric pressures may also be used. In one embodiment, avacuum is placed upon the oven chamber, by reducing the pressure toabout 76 torr. In other embodiments, similar reduced pressures may beused. Suitable pressures range from a vacuum, i.e. about 10⁻⁵ to about10⁻⁷ torr, to at least about 2 atmospheres, i.e., about 1540 torr.Suitable flow rates range from a flow rate sufficient to produce fromabout 1 atmospheric exchange per hour to a flow rate sufficient toproduce at least about 20 atmospheric exchanges per hour, determined bythe volume of the chamber and the flow rate of gas.

Further variables of properties of the inorganic powder which affecttime and temperature for the debinding steps for a particular greencomposition are: particle size, particle morphology, percent porosityand continuity of porosity. The effects of these variable are complex,and some testing may be required to obtain the optimum for each of theseproperties for a given inorganic powder and binder compositioncombination used in a green composition. For example, decreased particlesize increases the surface area which in turn increases thesinterability to produce fully dense parts. When particles are moreclosely packed, less porosity is formed and the likelihood of porecontinuity decreases. This means the binder composition will be retardedin finding a means of escape from the part as the debinding processproceeds. Thus, the result of smaller inorganic powder particle size islikely to be a longer debind time, since the temperature increases maybe required to proceed at a reduced rate of increase.

A further variable which affects time and temperature for the debindingsteps for a particular green composition is the chemical nature of theinorganic powder. A powder may tend to act as an activator, or even likea catalyst, in the decomposition of one or more of the components of abinder composition, and so may result in faster debinding of thosecomponents. Alternatively, if the inorganic powder is a relatively inertmaterial, such as alumina, Al₂O₃, the primary factors affecting thedebinding process are the temperature, time and atmosphere of thedebinding.

Some inorganic powders, such as molybdenum, tungsten and alumina, haverelatively high sintering temperatures, which are significantly higherthan the debinding temperature of the guanidine wetting agent, which isthe last of the ingredients, polycarbonate polymer, ethylenebisamide waxand guanidine wetting agent, to debind. It is such situations which thedebinding extender additive embodiment of the present invention isintended to address. By addition of the debinding extender, a portion ofthe binder composition remains up to temperatures of about 850° C.,allowing a significantly higher temperature to be attained with at leasta portion of the binder present to maintain the inorganic powder inposition until sintering begins extending the debinding process. Thus,this feature of the present invention provides added versatility to theselection of components for the binder composition and green compositionin PIM processes.

Similarly, it may be advantageous to use an additive such as thedebinding accelerator, in order to save significant amounts ofproduction time. The debinding accelerator increases the rate at whichthe polycarbonate polymer is decomposed during the debinding, andthereby saves time in the debinding process. The debinding acceleratorfacilitates achieving the “no-ash” feature of the present invention, byfacilitating decomposition and loss of the polycarbonate polymer fromthe green composition. The formation of, e.g., carbonaceous residues maybe considered “ash”, since such residues are an impurity in the sinteredpart. The debinding accelerator helps to avoid formation of carbides,which also may result from formation of carbonaceous impurities in thesintered part. When the part includes, e.g., tungsten in the inorganicpowder, the presence of elemental carbon with the tungsten at sinteringtemperatures may give rise to rapid formation of tungsten carbide. Othercarbide-forming metals may also form carbides if carbonaceous impuritiesare formed due to the decomposition of the polycarbonate polymer. Use ofthe debinding accelerator may help to avoid such possible problems.

Alternatives to the preparation of green parts as described above by PIMinclude pressing the green composition into a mold for P&S, followed bya sintering step. Alternatively, the blended green composition can beextrusion - or ejection-molded to form a green body, or the green bodycan be prepared by casting the mixture on a tape. The green body mayalso be prepared by spray-drying rotary evaporation, etc. Following theformation of the blended green composition into the desired shape, theshaped mass is subjected to the above described elevated temperaturetreatments. These treatments first eliminate the binder composition, asdescribed more fully above, and then sinter the inorganic powdersresulting in the formation of a shape having the desired propertiesincluding suitable densities.

For metal powders, the sintering generally occurs between about 400° C.to about 2100° C. Typically for many metals, to about 1000° C. Forceramic processes, the sintering generally occurs from about 600° C.,preferably about 700° C. up to about 1700° C. Of course, the sinteringtemperature is characteristic of the particular inorganic powder used inthe green composition, and may be affected by impurities or additives.For example, carbonyl iron is frequently doped with nickel, at the levelof, for example, about 2 wt %, as a sintering aid. The presence of thenickel allows the sintering to take place at a lower temperature and/orin a shorter amount of time than would otherwise be required forcarbonyl iron. When the inorganic powders are oxide powders, baking andsintering can be effected in the presence of oxygen. When the inorganicpowders are non-oxide powders such as the nitrides and carbides,sintering is effected in a nonoxidizing atmosphere such as an atmosphereof hydrogen, argon or nitrogen gas.

The debinding step takes place at moderately elevated temperatures, andis generally completed by ramping to a series of temperatures belowabout 700° C. When a debinding extender is present, the ramping to aseries of increased temperatures may go to at least about 850° C. aspart of the debinding steps. It is the debinding steps which are theprimary focus of the present invention.

Removal of the organic materials of the binder composition is generallycompleted before the inorganic powders are subjected to sintering. Inthis process, substantially all of the binder composition is removed.Some of the binder composition materials may remain at the time thesintering begins, although the amount is relatively small. Theseremaining portions of the binder composition will be essentiallycompletely removed in the sintering steps, depending of course, onfactors such as the decomposition temperature of the remaining bindercomponent, the sintering temperature and the sintering atmosphere. In acase in which the additive is present in the form of an debindingaccelerator dispersed on a solid carrier, if the carrier is one such ascalcium carbonate or silica, the Ca or Si will remain after debindingand sintering. Since the solid carrier is normally present in very lowconcentrations, i.e., about 5-10 wt % of the total weight to thedebinding accelerator, the impurity effect due to the presence of theseelements is generally small, since the debinding accelerator is added ina relatively small amount compared to the composition as a whole.

Each of the ingredients of the binder composition, the polycarbonatepolymer, the ethylenebisamide, the guanidine wetting agent and theadditive(s), may be initially formed in a solid, pelletized form. Toform the pellets, these ingredients are combined and heated to melting,at approximately 100° C., in the manner indicated above. The ingredientsare at least partially miscible with each other, so that when activelymixed in a twin screw compounding extruder at approximately 100° C., thebinder composition is homogenous or almost homogenous, and the bindercomposition quickly and easily forms a uniform, albeit heterogeneous,mixture with a minimum of shear. Thus, the binder composition forms auniform heterogeneous mixture with only one extrusion cycle. In onespecific case, the liquid binder composition was mixed at a temperatureof approximately 100° C. to form a uniform heterogeneous mixture within10 minutes of extrusion.

The heated heterogeneous liquid mixture of the binder composition may bemixed with the inorganic powder to form the green composition. Themixing of the binder composition and inorganic powder to form the greencomposition is best undertaken in the twin screw compounding extruder,which, among other benefits, results in thorough mixing with a minimumof exposure of the green composition components to atmospheric air. Suchexposure may be deleterious to either or both the binder composition andthe inorganic powder.

The green composition, when mixed at a temperature of about 100° C. forma liquid with a viscosity of between 5 and 300 Pascal-seconds dependingon the shear rate. As the shear rate increases, the viscosity generallydecreases to some degree, although as would be understood, there is alimit to the decrease.

The heated green composition may be extruded at approximately 100° C. toform feedstock pellets. The feedstock pellets, once made, may beinjection molded at any subsequent time by heating to a temperature ofapproximately 100° C. and pumping into a mold to make a green part,which is also known as a compact of a part. The resulting green part isthen subjected to the series of temperature increases to debind thecompact and thence to sinter the inorganic powder, as has been describedabove.

In one embodiment, the method includes, in step (d), a plurality oftemperature increases to elevated temperatures. In one embodiment, themethod includes maintaining each of the elevated temperatures constantfor a period of time. In one embodiment of the method, the elevatedtemperatures correspond to temperatures at which individual ingredientsof the binder composition are debound. In one embodiment, the elevatedtemperatures include a first elevated temperature which corresponds tothe debinding temperature of the polycarbonate polymer, a secondelevated temperature which corresponds to the debinding temperature ofthe ethylenebisamide wax, and a third elevated temperature whichcorresponds to the debinding temperature of the guanidine wetting agent.In one embodiment, the third elevated temperature is higher than thesecond elevated temperature, and the second elevated temperature ishigher than the first elevated temperature. In one embodiment, theadditive is a debinding extender which debinds at a fourth elevatedtemperature, which is higher than the first, second or third elevatedtemperatures. In all cases, the binder composition debinds in an orderwhich is the reverse of prior art debinding, and is referred toconveniently as reverse debinding. Even though when the debindingextender is present, and it debinds last, the order of debinding of theother three components, the polycarbonate, the ethylenebisamide and theguanidine, is in a reverse order. Thus, the debinding process isconsidered to be reverse

Debinding of the compact may be completed when the temperature of thecompact reaches about 600° C. The temperature should be maintained atthis level for a period of up to about 12 hours. This heating processremoved the binder composition from the compact. The compact was thensintered by heating the compact to a temperature of approximately 1,650°C. for a period of up to 4 hours. The resulting product is a part madeof the inorganic material of which the inorganic powder had been made.

FIG. 2 is a schematic engineering drawing of one screw 60 of a twinscrew compounding extruder 62 in accordance with one embodiment of theinvention. The twin screw compounding extruder 62 shown in FIG. 2 is aschematic depiction of a Leistritz 18 mm twin screw compoundingextruder, which is used in one embodiment of the method of the presentinvention. The Leistritz twin screw compounding extruder 62 provides ahigh level of combining and compounding the components of the greencomposition of the present invention. As shown in FIG. 2, the twin screwextruder 62 includes a main feed 64, a secondary feed 66 and a vent 68.In one embodiment, the binder composition is fed into the main feed 64and the inorganic powder is fed into the secondary feed 66. The vent 68is provided to vent entrapped gases and to maintain the internalpressure in the twin screw compounding extruder 62 at a desired level.

EXAMPLES

The following exemplary formulations are intended to provide a betterunderstanding of the invention, and are not intended as limiting.

Example 1

A green composition comprising a binder composition and an inorganicpowder comprising 98% carbonyl iron doped with 2% nickel as a sinteringaid, according to the present invention, is prepared as follows.

The binder composition is as follows:

poly(propylene carbonate) Q-PAC ™ 40  59.43 wt % ethylenebisstearamideACRAWAX ® C  25.15 wt % guanidine ethyl hexanoate  8.49 wt % guanidinestearate  6.94 wt % Total 100.0

The above binder composition does not include either additive, thedebinding accelerator or the debinding extender. The binder compositionis prepared by combining the ingredients in a twin screw compoundingextruder, heating to about 100° C. for about 10 minutes, until themixture is substantially homogenous, and then pelletizing the bindercomposition in, e.g., a strand cutter pelletizing apparatus. This bindercomposition is designated APEX™ 201.

The ingredients for the green composition, comprising 59 vol % carbonyliron/nickel and 41 vol % of pellets of the above binder composition arecombined, compounded and pelletized in a twin screw compounding extruderas described above. Expressed on a weight basis, the green compositioncomprises 91 wt % carbonyl iron/Ni and 9 wt % of the above bindercomposition. After the green composition is thoroughly compounded, it isextruded and pelletized. The pellets are subsequently fed into aninjection molding machine, and injected into a mold. The debindingprofile of Example 1 is shown below in Table 1 and in FIG. 3.

TABLE 1 Elapsed Step Time, Time, No. Action in Step min. min. 21 Heatfrom RT @  75° C./hr to 110° C. 68  68 22 Soak (hold) @ 110° C. 60 12823 Heat from 110° C. @  75° C./hr to 140° C. 18 146 24 Heat from 140° C.@ 100° C./hr to 190° C. 40 186 25 Soak (hold) @ 190° C. 60 246 26 Heatfrom 190° C. @ 150° C./hr to 425° C. 94 340 27 Soak (hold) @ 425° C. 60400 28 Heat from 425° C. to sintering temperature

In FIG. 3 and Table 1, the poly(propylene carbonate) is debound in steps23, 24 and 25, a total of 118 minutes. The ethylenebisstearamide isdebound in step 26. The guanidine wetting agent is debound in steps 26and 27. Following substantially complete debinding, and the end of step27, at an elapsed debinding time of 400 minutes, the part is sintered byheating in step 28 at the rate of 300° C./hr to a sintering temperatureof 1425° C. In the steps 21 to 26, the atmosphere is hydrogen at apressure of 780 torr. In the steps 27 and 28, the chamber is held undera vacuum of about 10⁻⁶ torr.

Example 2

A green composition comprising a binder composition and silica,according to the present invention, is prepared as follows.

The binder composition is as follows:

poly(propylene carbonate) Q-PAC ™ 40  51.43 wt % ethylenebisstearamideACRAWAX ®C  25.15 wt % guanidine ethyl hexanoate  6.49 wt % guanidinestearate  6.94 wt % 2,5-dimethyl-2,5-di(t-butylperoxy)hexane  10.00 wt %Total 100.00 wt %

The binder composition is prepared by combining the ingredients in atwin screw compounding extruder, heating to about 100° C. for about 10minutes, until the mixture is substantially homogenous, and thenpelletizing the binder composition in, e.g., a strand cutter pelletizingapparatus. This binder composition is designated APEX™ 203.

The ingredients for the green composition, comprising 65 vol % silicaand 35 vol % of pellets of the above binder composition are combined,compounded and pelletized in a twin screw compounding extruder asdescribed above. Expressed on a weight basis, the green compositioncomprises 77 wt % silica and 23 wt % of the above binder composition.After the green composition is thoroughly compounded, it is extruded andpelletized. The pellets are subsequently fed into an injection moldingmachine, and injected into a mold. The debinding profile of Example 2,in which the additive is present in the form of an debindingaccelerator, is shown below in Table 2 and in FIG. 4.

TABLE 2 Elapsed Step Time, Time, No. Action in Step min. min. 21 Heatfrom RT @  75° C./hr to 110° C. 68  68 22 Soak (hold) @ 110° C. 20  8823 Heat from 110° C. @ 100° C./hr to 190° C. 54 142 24 Soak (hold) @190° C. 30 172 25 Heat from 190° C. @ 150° C./hr to 425° C. 94 266 26Soak (hold) @ 425° C. 30 296 27 Heat from 425° C. to sinteringtemperature

In FIG. 4 and Table 2, the poly(propylene carbonate) is debound in steps23 and 24, a total of 84 minutes. As can be observed by comparison ofsteps 23 and 24 in FIG. 4 and Table 2 with steps 23, 24 and 25 in FIG. 3and Table 1, the time for debinding the poly(propylene carbonate) issubstantially reduced, from 118 to 84 minutes, thus reducing the overalldebinding time. The ethylenebisstearamide is debound in step 25. Theguanidine wetting agent is debound in steps 26 and 27. Followingsubstantially complete debinding, at the end of step 27 at an elapseddebinding time of 296 minutes, the part is sintered by heating in step27 at the rate of 300° C./hr to a sintering temperature of 1425° C. Inthe steps 21 to 25, the atmosphere is hydrogen at a pressure of 780torr. In the steps 26 and 27, the chamber is held under a vacuum ofabout 10⁻⁶ torr. Thus, by addition of the organic peroxide debindingaccelerator, the pre-sintering time is reduced from 400 minutes to 296minutes. This time may be further reduced by increasing the rate oftemperature increase in step 21.

Example 3

A green composition comprising a binder composition and titanium,according to the present invention, is prepared as follows.

The binder composition is as follows:

poly(propylene carbonate) Q-PAC ™ 40  52.43 wt % ethylenebisstearamideACRAWAX ®C  20.15 wt % guanidine ethyl hexanoate  8.49 wt % guanidinestearate  6.94 wt % atactic polypropylene M_(n) ≅ 50,000  12.00 wt %Total 100.00 wt %

The binder composition is prepared by combining the ingredients in atwin screw compounding extruder, heating to about 100° C. for about 10minutes, until the mixture is substantially homogenous, and thenpelletizing the binder composition in, e.g., a strand cutter pelletizingapparatus. This binder composition is designated APEX™ 204.

The ingredients for the green composition, comprising 59 vol % titaniumand 41 vol % of pellets of the above binder composition are combined,compounded and pelletized in a twin screw compounding extruder asdescribed above. Expressed on a weight basis, the green compositioncomprises 86 wt % titanium and 14 wt % of the above binder composition.After the green composition is thoroughly compounded, it is extruded andpelletized. The pellets are subsequently fed into an injection moldingmachine, and injected into a mold. The debinding profile of Example 3,in which the additive is present in the form of a debinding extender, isshown below in Table 3 and in FIG. 5.

TABLE 3 Elapsed Step Time, Time, No. Action in Step min. min. 21 Heatfrom RT @  75° C./hr to 110° C. 68  68 22 Soak (hold) @ 110° C. 60 12823 Heat from 110° C. @  75° C./hr to 190° C. 18 146 24 Heat from 140° C.@ 100° C./hr to 190° C. 40 186 25 Soak (hold) @ 190° C. 60 246 26 Heatfrom 190° C. @ 150° C./hr to 425° C. 94 340 27 Soak (hold) @ 425° C. 60400 28 Heat from 425° C. @ 150° C./hr to 560° C. 65 465 29 Soak (hold) @560° C. 50 515 30 Heat from 560° C. to sintering temperature

In FIG. 5 and Table 3, the poly(propylene carbonate) is debound in steps24 and 25. The ethylenebisstearamide is debound in step 26. Theguanidine wetting agent is debound in steps 26 and 27. The debindingextender, atactic polypropylene having a number average molecular weight(M_(n)) of about 50,000, is debound in steps 28 and 29. As can beobserved from a comparison of the debinding profile of FIG. 5 and Table3 with that of FIG. 3 and Table 1, the debinding extender portion of thebinder composition remains present at a higher temperature and for alonger period, until it is debound at a temperature of about 560° C.,after an elapsed time of 515 minutes. This is a substantially highertemperature and longer time than would be observed for a bindercomposition such as that of Examples 1 and 2, which do not include adebinding extender. Following substantially complete debinding, and theend of step 29, at an elapsed debinding time of 580 minutes, the part issintered by heating in step 30 at the rate of 300° C./hr to a sinteringtemperature of 1425° C. In the steps 21 to 26, the atmosphere ishydrogen at a pressure of 780 torr. In the steps 27-30, the chamber isheld under a vacuum of about 10⁻⁶ torr.

Example 4

A green composition comprising a binder composition and zirconia,according to the present invention, is prepared as follows.

The binder composition is as follows:

poly(propylene carbonate) Q-PAC ™ 40  45.43 wt % ethylenebisstearamideACRAWAX ®C  20.15 wt % guanidine ethyl hexanoate  6.48 wt % guanidinestearate  5.94 wt % 2,5-dimethyl-2,5-di(t-butylperoxy)hexane  10.00 wt %atactic polypropylene M_(n) ≅ 50,000  12.00 wt % Total 100.00 wt %

The binder composition is prepared by combining the ingredients in atwin screw compounding extruder, heating to about 100° C. for about 10minutes, until the mixture is substantially homogenous, and thenpelletizing the binder composition in, e.g., a strand cutter pelletizingapparatus. This binder composition is designated APEX™ 205.

The ingredients for the green composition, comprising 65 vol % zirconiaand 35 vol % of pellets of the above binder composition are combined,compounded and pelletized in a twin screw compounding extruder asdescribed above. Expressed on a weight basis, the green compositioncomprises 88 wt % zirconia and 12 wt % of the above binder composition.After the green composition is thoroughly compounded, it is extruded andpelletized. The pellets are subsequently fed into an injection moldingmachine, and injected into a mold. The debinding profile of Example 4,in which the additive is present in the form of both an debindingaccelerator and a debinding extender, is shown below in Table 4 and inFIG. 6.

TABLE 4 Elapsed Step Time, Time, No. Action in Step min. min. 21 Heatfrom RT @  75° C./hr to 110° C. 68  68 22 Soak (hold) @ 110° C. 20  8823 Heat from 140° C. @ 100° C./hr to 190° C. 54 142 24 Soak (hold) @190° C. 30 172 25 Heat from 190° C. @ 150° C./hr to 425° C. 94 266 26Soak (hold) @ 425° C. 30 296 27 Heat from 425° C. @ 150° C./hr to 560°C. 65 361 28 Soak (hold) @ 560° C. 50 411 29 Heat from 560° C. tosintering temperature

In FIG. 6 and Table 4, the poly(propylene carbonate) is debound in steps23 and 24, a total of 118 minutes. As can be observed by comparison ofsteps 23 and 24 in FIG. 6 and Table 4 with steps 23-25 in FIG. 2 andTable 1, the time for debinding the poly(propylene carbonate) issubstantially reduced, from 118 to 84 minutes, thus reducing the overalldebinding time. The ethylenebisstearamide is debound in step 25. Theguanidine wetting agent is debound in steps 26 and 27. The debindingextender, atactic polypropylene having a number average molecular weight(M_(n)) of about 50,000, is debound in steps 27 and 28. As can beobserved from the debinding profile, the debinding extender portion ofthe binder composition remains present at a higher temperature and for alonger period, until it is debound at a temperature of about 560° C.,after an elapsed time of 411 minutes. This is a substantially highertemperature and longer time than would be observed for a bindercomposition such as that of Examples 1 and 2, which do not include adebinding extender. Following substantially complete debinding, and theend of step 29, at an elapsed debinding time of 411 minutes, the part issintered by heating in step 29 at the rate of 300° C./hr to a sinteringtemperature of 1425° C., and holding. In the steps 21 to 25, theatmosphere is hydrogen at a pressure of 780 torr. In the steps 26-29,the chamber is held under a vacuum of about 10⁻⁶ torr.

A wide variety of parts can be made by PIM in accordance with thepresent invention. Such parts include for example, for an inorganicpowder which is a metal, gun parts, shear clipper blades and guides,watch band parts, watch casings, coin feeder slots, router bits, drillbits, disk drive magnets, VCR recording heads, jet engine parts,orthodontic braces and prostheses, dental brackets, orthopedic implants,surgical tools and equipment, camera parts, computer parts, and jewelry.Such parts include for example, for intermetallic inorganic powders,turbochargers, high temperature insulators, spray nozzles and threadguides. Such parts include for example, for ceramic inorganic powders,optical cable ferrules, ski pole tips, haircutting blades, airfoilcores, piezoelectric (e.g., lead zircon titanate, PZT) parts, oxygensensors and spray nozzles.

Binder Compositions for Press & Sinter Applications

The binder composition of the present invention may also be used forpress & sinter applications. In press & sinter application, theinorganic powder loading is considerably higher than in PIM. Thetrade-off for the higher loading is the limitation that the parts madeby a press & sinter process are quite limited in complexity. In fact,press & sinter can be considered to be limited to quite simple parts.The types of inorganic powders which can be used in press & sinterapplications are more limited, due to the requirement that the powdersbe sufficiently malleable and compactable to be useable in press &sinter applications. Powders having a high hardness values, such as forexample WC, are generally not useable in press & sinter applications.The hardness value becomes an issue in press & sinter applications dueto the low binder loadings used in press & sinter as compared to PIM.

In a press & sinter application, the loading of the binder compositionin the green composition is typically in the range from about 1% byvolume to about 10% by volume of the green composition from which thepart will be formed. (As with PIM applications, the green composition ismeasured on a volume basis, with the loadings expressed in volumepercentages.) In one embodiment, the loading of the binder compositionis 1% by volume. In one embodiment, the loading of the bindercomposition is 2% by volume. In one embodiment, the loading of thebinder composition is 3% by volume. In one embodiment, the loading ofthe binder composition is 4% by volume. In a press & sinter process, thegreen composition is pressed into the desired shape by means of, e.g., ahydraulic press. Once the part is pressed into its shape, it has a greenstrength in the range from about 1,000 psi (about 70 Kg/cm²) to about4,000 psi (about 281 Kg/cm²). The part is then sintered.

For a press & sinter application, the binder composition according tothe present invention has the following ranges of components (aspreviously, the binder composition is prepared on a weight by weightpercentage bases (wt %)).

polycarbonate polymer  10-50 wt % ethylenebisamide wax  30-70 wt %guanidine wetting agent   5-30 wt % additive 0.1-20 wt %

For press & sinter applications, the foregoing descriptions with respectto the selection of polycarbonate polymer, ethylenebisamide wax andguanidine wetting agent continue to apply. Thus, the acid used to formthe reaction product of guanidine and acid is selected on the basis ofthe isoelectric point of the inorganic powder. Similarly, the same rangeof inorganic powders can be used, as long as these are useable in apress & sinter application.

In view of the foregoing description, it is apparent that the presentinvention provides a new and improved binder which is formed and/or usedin accordance with a new and improved method.

What is claimed is:
 1. A binder composition comprising: a polycarbonatepolymer; an ethylenebisamide wax; a guanidine wetting agent; and anadditive which is a debinding accelerator or debinding extender.
 2. Thebinder composition of claim 1, wherein the additive is a debindingaccelerator which accelerates debinding.
 3. The binder composition ofclaim 2, wherein the debinding accelerator is an organic peroxide. 4.The binder composition of claim 3, wherein the organic peroxide is adialkyl peroxide.
 5. The binder composition of claim 3, wherein theorganic peroxide comprises at least one peroxide selected from dicumylperoxide, di-t-butylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,di-t-amylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,α,α′-di(t-butylperoxy)diisopropylbenzene, decanoyl peroxide, lauroylperoxide, succinic peroxide, 2-dihydroperoxybutane and multimersthereof, 2,4-pentanedione peroxide, di(n-propyl)peroxydicarbonate,di(sec-butyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate,1,1-dimethyl-3-hydroxybutyl peroxyneodecanoate, α-cumylperoxyneodecanoate, 1,1-dimethyl-3-hydroxybutyl peroxyneoheptanoate,α-cumyl peroxyneoheptanoate, t-amyl peroxyneodecanoate, t-butylperoxyneodecanoate, t-amyl peroxypivalate, t-butyl peroxypivalate,2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy)hexane,t-amylperoxy-2-ethylhexanoate, t-butyl peroxyacetate, t-amylperoxyacetate, t-butyl perbenzoate, t-amyl perbenzoate,O,O-t-amyl-O-(2-ethylhexyl)monoperoxycarbonate,di-t-butyIdiperoxyphthalate, t-butylcumylperoxide,O,O-t-butyl-O-(isopropyl)monoperoxycarbonate,2,5-dimethyl-2,5-di(benzoylperoxy)hexane,O,O-t-butyl-1-(2-ethylhexyl)monoperoxycarbonate, cumene hydroperoxide,t-butyl hydroperoxide, t-amyl hydroperoxide,1,1-di(t-butylperoxy)-3,3,5-trimethyl-cyclohexane,1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)cyclohexane,ethyl-3,3-di(t-butylperoxy)butyrate, andethyl-3,3-di(t-amylperoxy)butyrate,1,3-bis(t-butylperoxyisopropyl)benzene, 1,1-bis(t-butylperoxy)valerate,benzoyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoylperoxide, 3,5,5-trimethylhexanoyl peroxide, 2,4-dichlorobenzoylperoxide, m-toluyl peroxide, methylethylketone peroxide, cyclohexanoneperoxide, 3,5,5-trimethylhexanone peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylhexane, 1,1-bis(t-butylperoxy)-cyclohexane, 2,2-bis(t-butyl peroxy)octane, diisopropylbenzenehydroperoxide, diisopropyl peroxydicarbonate,t-butylperoxy-2-ethylhexanoate, t-butyl peroxy neodecanate, t-butylperoxy laurate, t-butyl peroxy isopropylcarbonate,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,2′-bis(t-butylperoxy)-diisopropylbenzene,4,4,′-bis(t-butylperoxy)butylvalerate, t-butylperterephthalate,2,2-di-(t-butylperoxy)butane, n-butyl 4,4′-di-t-butylperoxyvalerate,2,4-dichlorobenzoyl peroxide, o-chlorobenzoyl peroxide,t-butylperoxyneohexanoate, di-(3-methoxybutyl)peroxydicarbonate,4,4′-dichloro benzoyl peroxide, tert-butylperoxymaleic acid,2,4-pentanedione peroxide and2,5-dimethyl2,5-di(2-ethylhexanoylperoxy)hexane.
 6. The bindercomposition of claim 3, wherein the organic peroxide is2,5-dimethyl-2,5-di(t-butylperoxy)hexane.
 7. The binder composition ofclaim 3, wherein the organic peroxide is provided on a solid carrier. 8.The binder composition of claim 7, wherein the solid carrier is at leastone of a polyolefin, calcium carbonate, clay or silica.
 9. The bindercomposition of claim 2, wherein the debinding accelerator increases therate at which the polycarbonate debinds during debinding of the bindercomposition.
 10. The binder composition of claim 2, wherein thedebinding accelerator cleaves the polycarbonate polymer into polymericfragments.
 11. The binder composition of claim 2, wherein the debindingaccelerator is present in the range from about 0.01 wt % to about 10 wt% of the binder composition.
 12. The binder composition of claim 1,wherein the additive is a debinding extender which extends debinding.13. The binder composition of claim 12, wherein the debinding extenderis a polymer having a debinding temperature in the range from about 450°C. to about 750° C.
 14. The binder composition of claim 12, wherein thedebinding extender is at least one of polypropylenes orpolymethacrylates.
 15. The binder composition of claim 12, wherein thedebinding extender is a polymer having a weight average molecular weightin the range from about 25,000 to about 250,000.
 16. The bindercomposition of claim 15, wherein the polymer has a weight averagemolecular weight in the range from about 40,000 to about 120,000. 17.The binder composition of claim 14, wherein the polypropylene has aweight average molecular weight of about 50,000.
 18. The bindercomposition of claim 14, wherein the polymethacrylate has a weightaverage molecular weight of about 100,000.
 19. The binder composition ofclaim 12, wherein the debinding extender is present in the range fromabout 1 wt % to about 20 wt % of the binder composition.
 20. A greencomposition comprising the binder composition of claim 1, and aninorganic powder selected from a metal powder, a metal oxide powder, anintermetallic powder and a ceramic powder.
 21. The green composition ofclaim 20, wherein the binder composition is present in an amount in therange from about 30 vol % to about 60 vol % and the inorganic powder ispresent in an amount from about 70 vol % to about 40 vol %.
 22. Thegreen composition of claim 20, wherein the binder composition is presentin an amount in the range from about 1 vol % to about 10 vol % and theinorganic powder is present in an amount from about 99 vol % to about 90vol %.
 23. A method for forming a part by powder injection molding,comprising: (a) forming a green composition comprising a bindercomposition and an inorganic powder, wherein the binder compositioncomprises a polycarbonate polymer, an ethylenebisamide wax, a guanidinewetting agent and an additive; and (b) heating the green composition todebind the green composition, wherein the additive accelerates orextends step (b).
 24. The method of claim 23, wherein the inorganicpowder is selected from a metal powder, a metal oxide powder, anintermetallic powder and a ceramic powder.
 25. The method of claim 23,wherein the additive is a debinding accelerator which accelerates step(b).
 26. The method of claim 25, wherein the debinding accelerator is anorganic peroxide.
 27. The method of claim 26, wherein the organicperoxide is a dialkyl peroxide.
 28. The method of claim 23, wherein theadditive is a debinding extender which extends step (b).
 29. The methodof claim 28, wherein the debinding extender is a polymer having adebinding temperature in the range from about 450° C. to about 750° C.30. The method of claim 28, wherein the debinding extender is at leastone of polypropylenes or polymethacrylates.
 31. The method of claim 30,wherein the polymer is a polypropylene having a weight average molecularweight of about 50,000.
 32. The method of claim 30, wherein the polymeris a polymethacrylate having a weight average molecular weight of about100,000.
 33. The method of claim 23, wherein step (b) includes aplurality of temperature increases to elevated temperatures, and each ofthe elevated temperatures is maintained substantially constant for aperiod of time.
 34. The method of claim 33, wherein a first elevatedtemperature corresponds to the debinding temperature of thepolycarbonate polymer, a second elevated temperature corresponds to thedebinding temperature of the ethylenebisamide wax, and a third elevatedtemperature corresponds to the debinding temperature of the guanidinewetting agent.
 35. The method of claim 34, wherein the additive reducesthe time for debinding of the polycarbonate polymer.
 36. The method ofclaim 34, wherein the additive debinds at a fourth elevated temperature,said fourth elevated temperature being higher than said first, secondand third elevated temperatures.
 37. The method of claim 23, furthercomprising a step of transferring the flowable green composition into amold for a part.
 38. The method of claim 37, wherein step (b) comprisesheating the part to a temperature at which the binder compositiondebinds.
 39. The method of claim 38, further comprising a step ofheating the part to a temperature at which the powder is sintered. 40.The method of claim 38 wherein step (b) results in reverse debinding ofthe binder composition.
 41. The method of claim 23, wherein step (b)comprises heating the green composition to a plurality of elevatedtemperatures to debind the green composition by reverse debinding,wherein a first elevated temperature corresponds to the debindingtemperature of the polycarbonate polymer, a second elevated temperaturecorresponds to the debinding temperature of the ethylenebisamide wax,and a third elevated temperature corresponds to the debindingtemperature of the guanidine wetting agent.
 42. The method of claim 41,wherein the additive is a debinding extender and step (b) furthercomprises heating to a fourth elevated temperature which corresponds tothe debinding temperature of the debinding extender.
 43. The method ofclaim 23 wherein step (b) results in reverse debinding of the bindercomposition.